When A Heart Attack Is Not A Cardiac Arrest
The Blocked Pipe, the Electrical Storm, and Why the Difference Can Save a Life
By lim ju boo, alias lin ru wu (林 如 武)
Formerly, Regional Staff Officer for Training in Emergency Medicine
St. John Ambulance Malaysia
Summary Guidelines:
1. Never perform Cardiopulmonary Resuscitation (CPR) on someone who has a heart attack, who is conscious and breathing. Doing chest compressions on an awake person who is breathing normally can cause serious, unnecessary internal injuries and bone fractures.
2. Heart Attack vs. Cardiac Arrest. A heart attack is a circulation problem (a blocked artery cutting off blood to a part of the heart muscle), but the heart is usually still beating. Cardiac arrest is an electrical problem where the heart abruptly stops pumping entirely.
3. Start CPR immediately only if the person is unresponsive and either not breathing or only gasping irregularly (known as agonal breathing).
4. Hands-Only CPR: If you are untrained, performing continuous, rapid chest compressions without rescue breaths is the exact standard recommended by organizations like the American Heart Association.
There is a surprisingly common misunderstanding about two medical terms that are often used as though they mean the same thing: heart attack and cardiac arrest.
They are not the same.
Let me first write a very short summary between cardiac arrest and heart attack.
A heart attack and a cardiac arrest are not the same thing.
A heart attack is primarily a circulation problem: a coronary artery becomes blocked or severely restricted, depriving part of the heart muscle of oxygen and causing myocardial injury or death.
A cardiac arrest is primarily an electrical problem: the heart suddenly develops a rhythm that is unable to produce effective circulation, causing the person to become unresponsive and stop breathing normally.
In simple terms:
Heart attack = the heart's blood supply is blocked.
Cardiac arrest = the heart's pumping function suddenly fails.
The two conditions are different, but they can be closely connected. A heart attack can damage the electrical stability of the heart and trigger a cardiac arrest.
Why are the two so often confused?
Most people, including many doctors whom I know who are not involved in cardiology or emergency medicine, use the terms heart attack and cardiac arrest almost interchangeably. Others tell me a heart attack is just a layman term for cardic arrest.
The confusion is understandable because both conditions involve the heart, both can be fatal, and a heart attack can sometimes lead to cardiac arrest. But physiologically they represent two quite different failures.
Let me now explain in greater depths.
A heart attack, medically called an acute myocardial infarction (AMI), is primarily a problem of blood supply. A coronary artery becomes blocked or severely restricted, depriving part of the heart muscle of oxygen.
A cardiac arrest is primarily a problem of electrical activity and effective pumping. The heart suddenly develops a rhythm or condition in which it can no longer produce an effective circulation.
In its simplest form:
Heart attack: the pipe is blocked.
Cardiac arrest: the pump has suddenly stopped working effectively.
The two conditions are different, but they can be closely connected. A heart attack can trigger a dangerous cardiac arrhythmia and lead to cardiac arrest. But cardiac arrest can also occur without a preceding heart attack.
Understanding this distinction is not merely a matter of medical terminology. In a real emergency, it can determine what a bystander needs to do within the first few minutes.
My own encounter with this distinction
I was reminded of this difference again when I attended a course in trauma and emergency medicine for doctors and paramedics at the University Hospital, National University of Malaysia (HUKM) in the late 1990s.
At that time, emergency medicine and resuscitation practice were already evolving rapidly. Yet the confusion between "heart attack" and "cardiac arrest" was, and remains, widespread.
Even today, a person may say:
"He had a heart attack and his heart stopped."
That sentence may actually describe two separate events: a myocardial infarction followed by cardiac arrest.
To understand why, we need to look at the heart not merely as a muscle, but as a pump supplied by blood vessels and controlled by an electrical system.
1. A heart attack is principally a "plumbing" problem
The heart is a powerful muscular pump, but the heart muscle itself needs oxygen and nutrients.
That supply comes through the coronary arteries.
Over many years, atherosclerotic plaques may develop within these arteries. If a plaque becomes disrupted, a blood clot may form and suddenly obstruct the artery.
The result is myocardial ischaemia—insufficient blood flow to part of the heart muscle.
If the interruption is severe and prolonged, myocardial cells become irreversibly injured and die. This is a myocardial infarction, commonly called a heart attack.
Imagine a large water pump supplied by several pipes.
If one of the pipes becomes blocked, part of the pump may be starved of water even though the pump itself continues operating.
That is the essence of the "plumbing" analogy.
During most heart attacks, the heart continues to beat and pump blood. The patient may therefore remain conscious, may be able to speak, and will usually still have a pulse.
This is one of the most important differences from cardiac arrest.
A person having a heart attack may be very ill while still being conscious and apparently able to communicate.
Symptoms may include chest pressure or discomfort, shortness of breath, sweating, nausea, weakness, or discomfort spreading to the arm, shoulder, back, neck or jaw. Symptoms can vary considerably between individuals and may sometimes be relatively mild.
The danger, however, is that heart muscle is being damaged while the patient is still alive and conscious.
The longer the coronary obstruction persists, the greater the potential myocardial injury.
Modern treatment therefore aims to diagnose the acute coronary syndrome rapidly and restore coronary blood flow when appropriate, together with evidence-based antiplatelet, anticoagulant and other therapies. Depending upon the clinical situation, urgent coronary angiography and percutaneous coronary intervention (PCI) may be required.
The current framework is provided by the 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for the Management of Patients With Acute Coronary Syndromes, which covers contemporary management of myocardial infarction, including STEMI and NSTEMI.
2. Cardiac arrest is principally an electrical catastrophe
Cardiac arrest is fundamentally different.
The immediate problem is that the heart suddenly loses its ability to produce an effective circulation.
The heart has an extraordinarily sophisticated electrical system. Electrical impulses normally travel through the heart in a coordinated sequence, causing the atria and ventricles to contract rhythmically and efficiently.
But sometimes this electrical system becomes catastrophically disturbed.
One of the most important examples is ventricular fibrillation (VF).
Instead of the ventricles contracting together as a muscular pump, their electrical activity becomes chaotic. The ventricular muscle fibres effectively quiver rather than pump.
The consequence is an abrupt loss of effective cardiac output.
The brain and other vital organs are suddenly deprived of adequate blood flow.
The person collapses, becomes unresponsive and is not breathing normally. There may instead be occasional abnormal gasping, known as agonal breathing. Such gasping should not be mistaken for normal breathing.
Other cardiac-arrest rhythms include pulseless ventricular tachycardia, asystole and pulseless electrical activity. The treatment depends upon the rhythm, with defibrillation being appropriate for shockable rhythms such as VF and pulseless ventricular tachycardia.
Thus, while a heart attack may leave the pump running while part of its muscle is being starved of oxygen, cardiac arrest represents the sudden loss of effective pumping and circulation.
3. The simplest comparison
The distinction can be remembered in this way.
A heart attack is principally a blood-flow problem. A coronary artery becomes blocked or severely restricted, and part of the heart muscle becomes starved of oxygen. The heart usually continues beating. The patient may therefore be conscious, breathing and have a pulse. The emergency treatment is aimed at rapidly restoring coronary blood flow and limiting myocardial damage.
A cardiac arrest is an abrupt circulatory and electrical emergency. The heart is no longer producing effective circulation. The patient becomes unresponsive and is not breathing normally. Immediate CPR and rapid defibrillation when indicated become critical.
So:
AMI: the heart muscle is being starved.
Cardiac arrest: the body is being starved of circulation.
4. The two can be connected
The distinction becomes particularly interesting because one condition can cause the other.
An acute myocardial infarction can damage the electrical stability of the heart. Ischaemic and injured myocardium can become electrically unstable and generate dangerous ventricular arrhythmias.
Thus:
Coronary artery blockage → myocardial ischaemia/infarction → electrical instability → ventricular arrhythmia → cardiac arrest
But this sequence does not always occur.
Most people suffering a heart attack do not immediately go into cardiac arrest.
Conversely, cardiac arrest can occur for many reasons other than myocardial infarction, including primary electrical disorders, cardiomyopathies, severe electrolyte disturbances, respiratory failure, drowning and other critical conditions.
This is why the two terms should never be treated as synonyms.
5. What should we do when someone is having a heart attack?
Suppose a person develops crushing or unusual chest discomfort, becomes breathless, sweats heavily or develops other symptoms suggestive of an acute coronary syndrome.
The person is conscious.
He or she is breathing.
There is a pulse.
This is not cardiac arrest.
CPR should not be started simply because someone is having a heart attack while remaining conscious and breathing.
The appropriate response is to activate emergency medical services immediately and obtain urgent medical assessment.
An ECG - I shall write a separate article on ECG and its intepretation later, and appropriate blood tests, including cardiac troponin, may help establish the diagnosis and determine the appropriate treatment.
The modern message is simple:
Do not wait to see whether a suspected heart attack gets better. Seek emergency medical help immediately.
The 2025 acute coronary syndrome guideline emphasises rapid assessment and contemporary reperfusion and medical treatment strategies.
6. What happens when the heart suddenly stops?
Now consider a completely different situation.
A person suddenly collapses.
He or she is unconscious and does not respond when spoken to or gently stimulated.
The person is not breathing normally—or is only gasping.
This should be treated as cardiac arrest.
For an ordinary bystander, it is not necessary to spend precious time repeatedly trying to find a pulse.
The modern approach is deliberately simple:
Recognise the arrest → call emergency services → start CPR → obtain an AED → apply it as soon as possible → follow its instructions.
The 2025 American Heart Association (AHA) Adult Basic Life Support guideline emphasises early recognition, high-quality CPR and prompt AED use as central interventions for adult cardiac arrest.
This represents an important evolution from the emergency medicine many of us learnt decades ago.
7. CPR: keeping the circulation alive
Cardiopulmonary resuscitation, or CPR, does not normally "restart" a fibrillating heart.
Its immediate purpose is different.
Chest compressions generate some artificial blood flow.
When the chest is compressed and released repeatedly, blood is moved through the circulation. This helps maintain some perfusion of the brain and other vital organs while definitive treatment is being delivered.
That is why CPR is so important.
It buys time.
But CPR alone may not correct the underlying electrical catastrophe.
For a shockable rhythm such as ventricular fibrillation, the treatment that may actually restore an organised rhythm is defibrillation.
This is where the AED becomes so important.
8. The AED: the electrical answer to an electrical problem
An automated external defibrillator (AED) is one of the most important advances in modern public emergency medicine.
The machine does not require the rescuer to diagnose ventricular fibrillation by looking at an ECG.
Once attached to the person's chest, the AED analyses the cardiac rhythm.
If a shockable rhythm is present, it advises or delivers a defibrillating shock according to its design and instructions.
If a shock is not appropriate, it does not deliver one and instructs the rescuer to continue CPR.
The AED therefore brings a treatment that once belonged almost exclusively inside hospitals into the community.
Airports, shopping centres, sports facilities, workplaces and other public places may now have AEDs precisely because time to defibrillation matters enormously.
The current AHA guidance continues to emphasise prompt defibrillation together with high-quality CPR.
A useful way of remembering the relationship is:
CPR buys time.
The AED may restore the rhythm.
Neither should be regarded as simply replacing the other.
9. What happened to the old 15:2 CPR?
This is where some of us who learnt CPR many years ago may indeed have been left behind.
Earlier CPR teaching used different compression-to-ventilation ratios, including 15 compressions followed by 2 rescue breaths in certain circumstances.
In 2005, the AHA changed the recommended adult compression-to-ventilation ratio to 30:2. The purpose was to increase the proportion of time devoted to chest compression and reduce interruptions.
The current AHA guidance continues to recommend conventional CPR for trained rescuers using:
30 chest compressions → 2 rescue breaths → repeat.
The recommended compression rate for adults is approximately 100–120 compressions per minute, with a depth of at least 5 cm (2 inches) while avoiding excessive depth.
The old 15:2 sequence may still be used by earlier-trained medical emergency doctors, paramedics and first responders if they do not update themselves.
It is simply no longer the standard adult CPR ratio.
10. But what about hands-only CPR?
Here another important modern development enters the picture.
Not every rescuer is trained in rescue breathing.
Some people are uncomfortable giving mouth-to-mouth ventilation to a stranger. Others may not know how to do it or may be physically unable to do so.
For an adult or adolescent who suddenly collapses, hands-only CPR provides a practical alternative.
The rescuer calls emergency services and performs continuous chest compressions—pushing hard and fast in the centre of the chest—until help arrives or an AED becomes available.
The AHA supports hands-only CPR for appropriate untrained or unwilling / unable bystanders.
This is an extremely important public-health message because doing something is vastly better than standing helplessly beside a person in cardiac arrest.
11. Does chest compression also ventilate the lungs?
Here I think my own scientific and physiological logic which is the motto of my blog - is interesting, but it needs a little qualification.
Compression and release of the chest inevitably produce changes in pressure within the thorax, and some movement of air can occur if the airway is open.
However, this should not be interpreted as meaning that chest compression provides adequate ventilation.
The principal purpose of chest compression is to maintain circulation.
Adequate ventilation requires movement of air through an open airway and, in conventional CPR, is provided by rescue breaths.
This is why the current AHA recommendations distinguish between conventional CPR with breaths and hands-only CPR.
Nevertheless, in an adult who suddenly collapses from a presumed primary cardiac cause, hands-only CPR can provide valuable circulation during the early period of arrest while an AED and professional help are being obtained.
The practical message should therefore be:
If you cannot or will not give rescue breaths, do not do nothing. Start chest compressions.
That is quite different from saying:
Chest compressions alone provide adequate ventilation.
They do not.
12. Why the AED is particularly important for the lone rescuer
There is another practical problem that deserves recognition.
High-quality chest compression is exhausting.
A lone rescuer performing compressions at 100–120 per minute can become very tired, and as fatigue develops, the quality of the compressions may deteriorate.
A trained resuscitation team can rotate rescuers during CPR. A lone bystander cannot.
This makes the AED even more important.
But we should not conclude that CPR is therefore of little value.
The two interventions have different purposes.
CPR maintains some circulation while the problem is being treated.
Defibrillation can terminate a shockable electrical rhythm.
The current AHA guidelines identify early high-quality CPR and prompt defibrillation as the key interventions that improve outcomes in adult cardiac arrest.
The extraordinary development is that an ordinary member of the public can now potentially deliver the second intervention with the assistance of a machine that analyses the rhythm automatically.
That was a very different world from the one in which many of us first learnt resuscitation.
13. One pump, two catastrophes
Let us return once more to the plumbing analogy.
Imagine a large water pump supplying a building.
The pump requires:
a pipe system to supply it
and
an electrical system to operate it.
If a pipe supplying part of the pump becomes blocked, the pump may continue operating but part of the pump is deprived of its essential supply.
That resembles a heart attack.
But if the electrical control system suddenly fails, the pump loses its ability to circulate water effectively.
That resembles cardiac arrest.
The distinction can therefore be remembered as:
Heart attack: the pump is still running, but its own blood supply is being cut off.
Cardiac arrest: the pump has suddenly lost effective pumping function because its electrical or mechanical operation has catastrophically failed.
And sometimes the first problem causes the second.
14. The most important message for everyone
The distinction between AMI and cardiac arrest can ultimately be reduced to a few simple ideas.
A heart attack is principally a blood-supply problem affecting the heart muscle.
Cardiac arrest is an abrupt failure of effective circulation, often caused by a catastrophic electrical rhythm.
A heart attack can cause cardiac arrest, but the two are not synonymous.
A conscious person with a suspected heart attack needs emergency medical treatment, not CPR.
An unconscious person who is not breathing normally or is only gasping should be treated as being in cardiac arrest.
CPR should begin immediately, and an AED should be obtained and used as soon as possible.
For trained rescuers, conventional adult CPR remains 30 compressions followed by 2 breaths. For an untrained or unwilling / unable bystander, hands-only CPR is an important and potentially lifesaving alternative.
Perhaps the most useful three sentences to remember are:
HEART ATTACK — THE PIPE IS BLOCKED.
CARDIAC ARREST — THE PUMP HAS STOPPED WORKING EFFECTIVELY.
CPR BUYS TIME; THE AED MAY RESTORE THE RHYTHM.
The heart is an extraordinary organ because it is simultaneously a pump, a muscle, a circulatory organ and an electrically controlled machine.
A heart attack primarily attacks its blood supply.
Cardiac arrest destroys its ability to maintain circulation.
They may meet in the same patient, but they are not the same event.
Knowing that difference may not make someone a doctor— but in the few minutes before the ambulance arrives, it may make someone a lifesaver.
I hope I have effectively delivered the message by using so many simple analogies.
References
1. Kleinman ME, Buick JE, Huber N, et al. Part 7: Adult Basic Life Support: 2025 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2025;152(Suppl 2)–S478.
2. American Heart Association. Part 9: Adult Advanced Life Support: 2025 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2025.
3. Rao SV, O'Donoghue ML, Ruel M, et al. 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for the Management of Patients With Acute Coronary Syndromes. Circulation. 2025.
4. American Heart Association. 2025 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care: Adult Basic Life Support. American Heart Association.
5. American Heart Association. Cardiac Arrest vs. Heart Attack. American Heart Association.
6. American Heart Association. Heart Attack or Sudden Cardiac Arrest: How Are They Different? American Heart Association.
7. American Heart Association. High-Quality CPR. American Heart Association.
8. American Heart Association. History of CPR. American Heart Association. The 2005 guidelines introduced the 30:2 adult compression-to-ventilation ratio.
9. American Heart Association. What Is CPR? American Heart Association. Current guidance on conventional CPR and hands-only CPR.
