Cardiac arrest is a sudden loss of heart function caused by an electrical malfunction that stops the heart from beating effectively. Within seconds, blood stops flowing to the brain and other organs, and the person collapses, loses consciousness, and stops breathing normally. Without immediate treatment, it is fatal within minutes. About 9.1% of people who experience cardiac arrest outside a hospital survive to leave the hospital, making fast bystander response critical.
What Happens Inside the Heart
Your heart beats because of a tightly coordinated electrical system that tells each chamber when to contract. In cardiac arrest, that system short-circuits. The most common trigger is a dangerous rhythm called ventricular fibrillation, where the lower chambers of the heart quiver rapidly and chaotically instead of pumping blood. The heart hasn’t stopped moving entirely, but it’s no longer doing anything useful. No blood reaches the brain, lungs, or other organs.
This is why cardiac arrest kills so quickly. The brain can tolerate only a few minutes without oxygen before permanent damage begins. Every minute without treatment reduces the chance of survival.
Cardiac Arrest vs. Heart Attack
People often use these terms interchangeably, but they describe different emergencies. A heart attack is a plumbing problem: a blocked artery cuts off blood supply to part of the heart muscle. The heart keeps beating during a heart attack, but the muscle tissue fed by that artery starts to die. Cardiac arrest is an electrical problem: the heart’s rhythm breaks down and the heart stops pumping altogether.
The two are connected, though. A heart attack can damage the heart’s electrical system and trigger cardiac arrest. Many cardiac arrests happen in people with underlying coronary artery disease they didn’t know they had. But cardiac arrest can also strike without a heart attack ever occurring.
Causes and Risk Factors
Coronary artery disease is the most common underlying cause. Cholesterol builds up inside artery walls, forming plaque that restricts blood flow to the heart. Over time this damages the heart muscle and makes dangerous rhythms more likely. Most people who experience cardiac arrest outside a hospital had some form of heart disease, even if they were never diagnosed.
Other conditions that raise the risk include:
- Cardiomyopathy: disease of the heart muscle that weakens or thickens the walls, making irregular rhythms more likely
- Heart valve disease: leaking or narrowed valves force the heart to work harder, eventually stretching or thickening the chambers
- Heart failure: the heart can’t pump enough blood for the body’s needs, and complications can include cardiac arrest
- Inherited electrical disorders: conditions like long QT syndrome and Brugada syndrome cause the heart to beat in disorganized patterns
- Congenital heart defects: structural problems present from birth, which are a leading cause of cardiac arrest in children and adolescents
Cardiac arrest can also follow events that aren’t primarily heart-related. Drug overdose, drowning, choking, severe trauma, and poisoning can all cause a person to stop breathing, which leads to cardiac arrest if untreated. Diabetes and imbalances in blood electrolytes like potassium, magnesium, and calcium also increase risk.
Cardiac Arrest in Young Athletes
When a seemingly healthy young person collapses during a game, the cause is almost always an undetected heart condition. Hypertrophic cardiomyopathy, a genetic condition where the heart muscle is abnormally thick, accounts for 35% to 50% of sudden cardiac deaths in young athletes in the United States. It affects roughly 1 in 500 people in the general population, and death from it is most common under age 30, often as the very first sign of the disease.
Another cause unique to sports is commotio cordis, where a blow to the chest (from a baseball, hockey puck, or collision) strikes during a tiny vulnerable window of the heartbeat lasting just 10 to 20 milliseconds. That impact disrupts the heart’s electrical stability and triggers ventricular fibrillation. About half of commotio cordis cases occur in competitive athletes between 11 and 20 years old, most often in baseball, softball, ice hockey, football, and lacrosse.
Warning Signs
Cardiac arrest often strikes without warning. Many people simply collapse with no symptoms beforehand. But some experience brief warning signs in the seconds or minutes before losing consciousness: chest pain or pressure, sudden shortness of breath, heart palpitations, nausea, dizziness, or sudden weakness. These symptoms can be easy to dismiss, especially during physical exertion.
Once cardiac arrest occurs, the signs are unmistakable. The person is unconscious, unresponsive, has no pulse, and is either not breathing or gasping abnormally.
What to Do: CPR and AEDs
Cardiac arrest is one of the few medical emergencies where bystander action genuinely determines whether someone lives or dies. Call emergency services immediately, then start chest compressions. Hands-only CPR (no rescue breaths needed) means pushing hard and fast on the center of the chest at a rate of 100 to 120 compressions per minute, pressing down at least 2 inches deep. That rhythm roughly matches the beat of “Stayin’ Alive” by the Bee Gees, which is not a coincidence in CPR training.
If an automated external defibrillator (AED) is available, use it as quickly as possible. AEDs are designed for untrained bystanders. The device analyzes the heart’s rhythm and determines whether a shock is appropriate. It only delivers a shock for rhythms that can respond to one, specifically ventricular fibrillation and rapid ventricular tachycardia. The device’s rhythm detection is highly accurate, with a specificity of 99.8% for identifying shockable rhythms. You cannot accidentally shock someone who doesn’t need it.
What Happens After Survival
Surviving cardiac arrest is only the beginning. After resuscitation, doctors work to identify what caused the event. This typically involves blood tests, heart imaging, stress testing, and sometimes an electrophysiology study where wires are threaded into the heart through a vein to map its electrical activity. If there’s a family history of heart conditions, genetic testing may be recommended for both the survivor and close relatives.
Recovery varies widely depending on how long the brain went without oxygen. Many survivors deal with physical fatigue, muscle weakness, and soreness from chest compressions that can crack ribs. Changes in vision, speech, fine motor skills, and difficulty swallowing are also reported.
Brain-related effects are common and can be the most life-altering. Survivors frequently report problems with short and long-term memory, difficulty concentrating, trouble learning new things, and reduced ability to plan or organize daily tasks. These cognitive changes can persist for months or longer.
The emotional toll is significant too. Fear of another cardiac arrest, anxiety, depression, and a sense of increased dependence on others are widely reported. These feelings often coexist with gratitude and even elation at being alive, creating an emotional landscape that many survivors find disorienting. Support groups and rehabilitation programs designed for cardiac arrest survivors can help navigate this mix of physical, cognitive, and emotional challenges.