What Causes Sudden Cardiac Arrest (SCA)?

The most common cause of SCA is a dangerous and abnormal heart rhythm called ventricular fibrillation (VF). In VF, the electrical signals that control the lower chambers of the heart (ventricles) become chaotic. This sends the ventricles into fibrillation, an extremely rapid and irregular quivering that cannot effectively pump blood to the body.

With no blood getting to the brain, a person experiencing VF loses consciousness within seconds. SCA and death can follow within minutes unless the heart is quickly shocked back into its normal rhythm. This is done using a defibrillator (a machine that delivers an electrical shock to the heart). The vast majority of VF victims die from SCA before they reach a hospital. However, prompt action by bystanders to alert first responders, and begin CPR, can improve the outcome.