What is cardiac arrest?

Cardiac arrest is a sudden and unexpected loss of heart function. Unlike a heart attack, which involves a blockage in blood flow to the heart muscle, cardiac arrest is caused by a malfunction in the heart’s electrical system. This disruption halts the heart’s ability to pump blood, leading to an immediate crisis.

Once the heart stops beating, blood flow to the brain and other vital organs stops. Without fast intervention, irreversible damage — and death — can occur within minutes. Understanding how cardiac arrest affects the body, step by step, highlights the urgency of prompt action.

The first seconds

The moment cardiac arrest begins, the heart’s electrical activity becomes chaotic, usually due to a condition called ventricular fibrillation. This causes the ventricles — the heart's main pumping chambers — to quiver instead of contracting normally.

Within 1–2 seconds of the heart stopping:

  • Blood flow throughout the body ceases

  • Oxygen delivery to vital organs stops

  • The person collapses suddenly and loses consciousness

During this early window, the person is clinically dead — but revival is possible with immediate CPR and defibrillation.

Brain response within seconds

The brain is highly sensitive to oxygen deprivation. It relies entirely on a constant supply of oxygen-rich blood to function.

Within 4–6 seconds:

  • Brain cells begin to suffer from oxygen loss

  • The person becomes unresponsive

  • Breathing may stop or become gasping (agonal breathing)

Even brief interruptions in oxygen delivery can impair brain function. Agonal breaths may occur in the first minute, often mistaken for normal breathing, but they’re a sign of extreme distress.

Loss of consciousness

Because the brain is not receiving oxygen, the individual quickly loses consciousness. This typically occurs within 10–15 seconds of cardiac arrest onset.

Other signs include:

  • Slumped or limp body

  • Unresponsiveness to shouting or touch

  • No detectable pulse or effective breathing

From this point forward, survival depends entirely on external intervention — primarily high-quality chest compressions and rapid defibrillation.

Impact on the heart

Although the heart initiates cardiac arrest, it is also a victim. Without coordinated electrical activity, the heart’s pumping action fails.

Key effects include:

  • Ventricular fibrillation or asystole (flatline)

  • Decreased myocardial oxygen supply

  • Cellular death in heart tissue if blood flow isn’t restored

  • Higher chance of irreversible arrhythmias

If defibrillation isn’t performed promptly, the heart’s ability to recover diminishes with each passing minute.

Oxygen deprivation spreads

Once the heart stops, oxygenated blood can no longer circulate. Every organ is affected almost instantly.

Within 1–3 minutes:

  • Kidney function ceases

  • Liver and gastrointestinal systems shut down

  • Muscles lose function and tone

  • Skin may become pale or bluish

The entire body enters a state of shock, with vital processes collapsing due to lack of energy and oxygen.

Cellular damage begins

All cells in the body require oxygen and nutrients to function. Without circulation, cells begin to die rapidly.

  • Brain cells: irreversible damage starts within 4–6 minutes

  • Heart muscle cells: damaged after 20–30 minutes

  • Kidneys and liver: impaired within 30–60 minutes

The longer the arrest continues, the greater the damage — especially to brain and heart tissue, which are least tolerant to oxygen loss.

The immune system’s role

During cardiac arrest, the immune system enters a hyperactive state once blood flow is restored (if revival occurs). This sudden restoration — called reperfusion — can cause inflammation.

Effects include:

  • Release of inflammatory cytokines

  • Capillary leakage and tissue swelling

  • Organ damage due to oxidative stress

While intended to protect, this immune surge can worsen recovery by damaging healthy tissue.

Respiratory failure

The lungs depend on blood flow to exchange oxygen and carbon dioxide. With no circulation:

  • Oxygen cannot reach the bloodstream

  • Carbon dioxide builds up in the body

  • Acidosis (blood acidity) occurs

  • Lung tissue can begin to deteriorate

Even if breathing continues for a few moments (agonal breaths), it's ineffective without circulation to transport gases.

Kidneys and liver shut down

The kidneys and liver are critical for filtering waste and balancing body fluids. Both are highly vascular and depend on steady blood flow.

In cardiac arrest:

  • Kidneys stop filtering blood

  • Fluid and electrolyte imbalances occur

  • Liver stops processing toxins and nutrients

  • Toxins accumulate rapidly

If the person is resuscitated, temporary or permanent kidney and liver failure may follow.

Gastrointestinal effects

The digestive system also suffers during cardiac arrest. Lack of oxygen leads to:

  • Decreased gut motility

  • Damage to the intestinal lining

  • Risk of bacterial leakage into the bloodstream

  • Nausea or vomiting post-resuscitation

These issues can complicate recovery and increase the risk of sepsis or infection.

Skin and muscles

Skin changes are a visible sign of cardiac arrest:

  • Cool to the touch

  • Pale, grey, or bluish

  • Sweaty or clammy prior to collapse

Muscles become flaccid without blood supply, and prolonged arrest may result in muscle death (rhabdomyolysis) and release of toxins like myoglobin into the blood.

Neurological injury

The brain is the most vulnerable organ during cardiac arrest. Without oxygen, neurons begin dying within minutes.

Potential outcomes include:

  • Memory loss or confusion

  • Seizures

  • Coma

  • Permanent vegetative state

  • Brain death

The extent of damage depends on how long the brain is deprived of oxygen and how quickly CPR and defibrillation were performed.

What happens during CPR

When performed correctly, CPR (cardiopulmonary resuscitation) provides a small amount of blood flow to vital organs.

It can:

  • Delay cellular death

  • Maintain some brain and heart function

  • Increase the effectiveness of defibrillation

  • Buy time until professional help arrives

Even so, CPR alone cannot restart the heart — defibrillation or advanced medical support is needed.

Return of spontaneous circulation

If the heart is successfully restarted (called return of spontaneous circulation, or ROSC), blood flow returns, but the body is still in critical condition.

Challenges include:

  • Reperfusion injury to tissues

  • Post-cardiac arrest syndrome

  • Organ failure from earlier damage

  • Risk of recurring arrhythmias

Immediate intensive care is required to stabilize the patient and prevent further complications.

Post-arrest recovery

Recovery after cardiac arrest varies greatly. Some people make full recoveries, while others suffer long-term effects.

Common complications:

  • Cognitive impairment or memory problems

  • Physical weakness or paralysis

  • Psychological trauma or depression

  • Organ dysfunction (e.g., kidneys, liver)

Survivors often require rehabilitation, medications, and lifestyle changes to manage ongoing risks and regain quality of life.

Emotional and mental effects

Even if the body recovers, survivors may face emotional struggles, including:

  • PTSD or fear of recurrence

  • Anxiety about physical activity

  • Depression from cognitive or physical changes

Support from family, therapists, and cardiac rehab programs is essential for long-term healing.

Sudden death risk

If no intervention occurs, cardiac arrest typically results in death within 5–10 minutes. Irreversible brain damage is almost certain after 10 minutes without oxygen, even if the heart restarts later.

Without CPR or defibrillation:

  • The brain dies from lack of oxygen

  • Organs begin to break down

  • The body enters irreversible shock

This grim reality underscores the need for rapid emergency response and public education.

The importance of early action

Each minute matters. Immediate steps to take if someone collapses:

  • Check for responsiveness

  • Call emergency services

  • Begin chest compressions (CPR)

  • Use an AED if available

Survival rates improve dramatically when bystanders act quickly. Learning CPR is a powerful way to save lives.

Prevention strategies

While not all cases are preventable, you can reduce the risk of cardiac arrest by:

  • Controlling blood pressure, cholesterol, and diabetes

  • Exercising regularly and eating a heart-healthy diet

  • Avoiding smoking and excessive alcohol use

  • Managing stress and sleep disorders

  • Having regular heart screenings, especially with family history

For high-risk individuals, doctors may recommend medications or implantable devices like defibrillators (ICDs).

Conclusion

Cardiac arrest sends shockwaves through the entire body — starting with the heart and brain, then rippling to every vital system. The effects are rapid, devastating, and often irreversible without immediate action.

By understanding how cardiac arrest affects the body step-by-step, we’re better prepared to act fast, save lives, and support survivors on their road to recovery.

Knowledge, CPR training, and regular heart care are among our strongest tools in the fight against sudden cardiac death.