Sudden cardiac arrest signs and symptoms are immediate and drastic and include:

• Sudden collapse
• No pulse
• No breathing
• Loss of consciousness

Sometimes other signs and symptoms occur before sudden cardiac arrest. These might include:

• Chest discomfort
• Shortness of breath
• Weakness
• Palpitations

But sudden cardiac arrest often occurs with no warning.

A problem in your heart rhythm (arrhythmia) — the result of a problem with your heart's electrical system — is the usual cause of sudden cardiac arrest.

The heart's electrical system controls the rate and rhythm of your heartbeat. If something goes wrong, your heart can beat too fast, too slowly or irregularly (arrhythmia). Often these arrhythmias are brief and harmless, but some types can lead to sudden cardiac arrest.

The most common heart rhythm at the time of cardiac arrest is an arrhythmia in a lower chamber of your heart (ventricle). Rapid, erratic electrical impulses cause your ventricles to quiver uselessly instead of pumping blood (ventricle fibrillation).

Heart conditions that can lead to sudden cardiac arrest

Sudden cardiac arrest can happen in people who have no known heart diease. However, a life-threatening arrhythmia usually develops in a person with a pre-existing, possibly undiagnosed heart condition. Conditions include:

• Coronary artery disease. Most cases of sudden cardiac arrest occur in people who have coronary artery disease, in which your arteries become clogged with cholesterol and other deposits, reducing blood flow to your heart.
• Heart attack. If a heart attack occurs, often as a result of severe coronary artery disease, it can trigger ventricular fibrillation and sudden cardiac arrest. Also, a heart attack can leave scar tissue in your heart. Electrical short circuits around the scar tissue can lead to abnormalities in your heart rhythm.
• Enlarged heart (cardiomyopathy). This occurs primarily when your heart's muscular walls stretch and enlarge or thicken. Then your heart's muscle is abnormal, a condition that often leads to arrhythmias.
• Valvular heart disease. Leaking or narrowing of your heart valves can lead to stretching or thickening of your heart muscle. When the chambers become enlarged or weakened because of stress caused by a tight or leaking valve, there's an increased risk of developing arrhythmia.
• Congenital heart disease. When sudden cardiac arrest occurs in children or adolescents, it can be due to a heart defect that was present at birth (congenital heart disease). Adults who've had corrective surgery for a congenital heart defect still have a higher risk of sudden cardiac arrest.
• Electrical problems in the heart. In some people, the problem is in the heart's electrical system itself instead of a problem with the heart muscle or valves. These are called primary heart rhythm abnormalities and include conditions such as Brugada's syndrome and long QT syndrome.

Because sudden cardiac arrest is so often linked with coronary artery disease, the same factors that put you at risk of coronary artery disease can also put you at risk of sudden cardiac arrest. These include:

• A family history of coronary artery disease
• Smoking
• High blood pressure
• High blood cholesterol
• Obesity
• Diabetes
• A sedentary lifestyle

Other factors that might increase your risk of sudden cardiac arrest include:

• A previous episode of cardiac arrest or a family history of cardiac arrest
• A previous heart attack
• A personal or family history of other forms of heart disease, such as heart rhythm disorders, congenital heart defects, heart failure and cardiomyopathy
• Age — the incidence of sudden cardiac arrest increases with age
• Being male
• Using illegal drugs, such as cocaine or amphetamines
• Nutritional imbalance, such as low potassium or magnesium levels
• Obstructive sleep apnea
• Chronic kidney disease

When sudden cardiac arrest occurs, reduced blood flow to your brain causes unconsciousness. If your heart rhythm doesn't rapidly return to normal, brain damage occurs and death results. Survivors of cardiac arrest might show signs of brain damage.