Understanding sudden cardiac arrest

Sudden cardiac arrest (SCA) is a life-threatening emergency that occurs when the heart unexpectedly stops beating. This halts blood flow to the brain and other organs, leading to collapse, unconsciousness, and, without immediate treatment, death within minutes.

SCA is not the same as a heart attack, although the two can be related. While a heart attack is a blockage issue in the heart’s arteries, SCA is an electrical malfunction that causes the heart to stop pumping. Unfortunately, SCA often happens with little or no warning — making early recognition and prompt action crucial.

Why early detection matters

Time is everything in a sudden cardiac arrest. Every minute without cardiopulmonary resuscitation (CPR) or defibrillation decreases the chance of survival by 7% to 10%. Recognizing the subtle or early signs — even moments before collapse — can mean the difference between life and death.

Although many SCA episodes occur suddenly and without symptoms, some people may experience warning signs in the minutes, hours, or even days before the event. Understanding these signs gives you or someone you love a critical window to seek emergency help.

Common warning signs

Some people may have symptoms prior to sudden cardiac arrest. While not everyone will exhibit them, these warning signs are more common than previously believed — especially in high-risk individuals.

Typical warning signs include:

  • Chest pain or discomfort

  • Unexplained shortness of breath

  • Palpitations or racing heartbeat

  • Lightheadedness or dizziness

  • Fatigue or weakness

  • Nausea or vomiting

  • Sudden fainting or collapse

These symptoms are not always dramatic, but they may indicate that the heart is in distress. In some cases, symptoms are mistaken for anxiety, indigestion, or overexertion.

Sudden collapse

The hallmark of sudden cardiac arrest is a sudden, unexpected collapse. A person experiencing SCA will:

  • Lose consciousness immediately

  • Have no pulse

  • Stop breathing or gasp briefly

  • Appear lifeless or unresponsive

Unlike a seizure, the person will not twitch or jerk — instead, they may fall to the ground and remain still. If you witness this, call emergency services immediately and begin CPR.

No pulse or breathing

Once the heart stops beating, circulation to the body stops. Within seconds:

  • There is no detectable pulse

  • Breathing stops or becomes irregular (gasping or agonal breathing)

  • The skin may turn pale or bluish

  • Eyes may remain open and fixed

This is the most obvious and dangerous sign — if untreated, brain damage can occur in less than 5 minutes. Immediate CPR and defibrillation with an AED is the only chance for survival.

Shortness of breath

Difficulty breathing without a known cause, especially if it comes on suddenly, may be a red flag. This can occur alone or with chest discomfort.

Shortness of breath (dyspnea) may be due to:

  • Reduced oxygen levels in the blood

  • Fluid buildup in the lungs

  • Abnormal heart rhythms causing poor circulation

It’s especially concerning when accompanied by lightheadedness or a feeling of impending doom.

Chest discomfort

Pain, tightness, or pressure in the chest is one of the most well-known symptoms of heart problems. However, in the context of SCA, it may be:

  • Sudden and severe

  • Accompanied by shortness of breath

  • Radiating to the arms, jaw, or back

  • Lasting more than a few minutes or coming and going

Chest discomfort that worsens with physical activity or emotional stress should never be ignored.

Unexplained fatigue

Extreme fatigue or exhaustion without clear cause may precede cardiac arrest. It can be subtle but persistent.

Fatigue may result from:

  • Inadequate oxygen delivery due to heart dysfunction

  • Abnormal heart rhythms causing reduced blood output

  • Poor sleep caused by nighttime arrhythmias

Women, in particular, may experience fatigue and weakness as a primary sign before a cardiac event.

Dizziness or fainting

Feeling dizzy, lightheaded, or faint may signal that the brain is not getting enough blood — a warning that the heart is struggling.

  • Fainting (syncope) often occurs just before full cardiac arrest

  • It may happen during exercise, stress, or even at rest

  • People may feel flushed, disoriented, or “off” before collapsing

Fainting with no clear cause should be evaluated by a doctor, especially if you have heart disease or a family history of sudden death.

Heart palpitations

Palpitations — the sensation of a rapid, fluttering, or pounding heartbeat — may indicate a dangerous arrhythmia.

Although palpitations can be harmless, those linked to SCA often:

  • Start abruptly

  • Occur at rest or during sleep

  • Are accompanied by dizziness or chest pain

  • Cause anxiety or a sense of fear

If you frequently experience irregular or fast heartbeats, especially if they feel “off,” seek a cardiac evaluation.

Nausea and vomiting

Some people experience gastrointestinal symptoms like nausea, vomiting, or indigestion before cardiac arrest. This is more common in women.

These symptoms may be caused by:

  • Decreased blood flow to the digestive system

  • Referred pain from the heart to the upper abdomen

  • Stress hormones released due to heart strain

Because these signs are easily mistaken for a stomach bug or food poisoning, they often go unrecognized as cardiac-related.

Sleep disturbances

Unusual nighttime symptoms can also precede SCA:

  • Waking up short of breath

  • Sudden racing heart during sleep

  • Difficulty falling or staying asleep

  • Vivid dreams or nightmares involving drowning or suffocation

Sleep-related arrhythmias and sleep apnea are both risk factors for sudden cardiac events, particularly in people with heart disease or obesity.

Anxiety or sense of doom

Some individuals report a sudden, intense feeling that something is terribly wrong — sometimes called “impending doom.” This is often accompanied by other symptoms like shortness of breath or chest pressure.

This instinctive fear can be the body’s way of signaling that it is under serious threat. It is not always psychological and should be taken seriously.

Symptoms in high-risk groups

Certain groups are more likely to experience warning signs before SCA:

  • People with previous heart attacks

  • Individuals with heart failure or cardiomyopathy

  • Those with inherited arrhythmias (e.g., long QT syndrome)

  • Athletes with undiagnosed heart conditions

  • People with diabetes or kidney disease

In these individuals, symptoms may be more subtle but still indicate a looming emergency.

Silent cases without warning

Unfortunately, not all cases of sudden cardiac arrest come with symptoms. In fact, studies show that nearly 50% of SCA events occur without warning.

In these “silent” cases:

  • The first sign may be sudden collapse

  • The person may have seemed fine moments before

  • There is no time for self-reporting or calling for help

This is why prevention and screening are just as important as symptom recognition.

What to do if you notice symptoms

If you or someone else experiences any of the above symptoms, take immediate action:

  • Call emergency services (911 or your local number)

  • Do not drive yourself to the hospital if symptoms are severe

  • Rest while waiting for help — do not ignore or “wait it out”

  • If the person collapses, start CPR and use an AED if available

Remember: time is critical in saving a life.

Prevention tips

Even without symptoms, there are steps you can take to reduce your risk of sudden cardiac arrest:

  • Get regular heart screenings, especially if you have risk factors

  • Manage conditions like high blood pressure, cholesterol, and diabetes

  • Avoid smoking, heavy alcohol use, and illegal drugs

  • Stay physically active — but talk to a doctor before starting intense workouts

  • Learn CPR and how to use an AED — you may save someone else’s life

In some cases, doctors may recommend medications or implantable cardioverter defibrillators (ICDs) for individuals at high risk.

When to see a doctor

Don’t wait until a crisis occurs. Schedule a medical checkup if you experience:

  • Recurring chest pain or discomfort

  • Frequent palpitations or fainting

  • Family history of sudden death

  • Known heart disease or heart failure

Early detection can prevent a fatal event and may give you access to life-saving interventions.

Conclusion

Sudden cardiac arrest is a frightening and deadly condition, but it’s not always without warning. Learning the signs — and acting quickly when they appear — can dramatically increase survival rates.

Whether you’re experiencing chest discomfort, palpitations, fainting, or just a strange sense that something is wrong, listen to your body. It might be trying to tell you something very serious.

By staying informed, maintaining heart health, and being ready to respond, you can help protect yourself and others from this silent killer.