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What is a Heart Attack?

A heart attack (or myocardial infarction) occurs when one or more of the arteries delivering blood to the heart is blocked. Oxygen in the blood cannot reach the heart muscle, and the heart muscle becomes damaged. This can cause heart failure at the time of the blockage; it can also cause progressive deterioration and failure of the heart months to years after the initial heart attack. A heart attack can also disturb the heart's electrical system. Malfunction of the heart's electrical system may cause dangerously fast heart rhythms that can lead to Sudden Cardiac Arrest (SCA).

What is a Sudden Cardiac Arrest?

SCA occurs when the heart's lower chambers (ventricles) suddenly develop a rapid, irregular rhythm (ventricular fibrillation) causing the ventricles to quiver rather than contract. The chaotic quivering motion of the ventricles renders the heart an ineffective pump that can no longer supply the body and brain with oxygen.Within seconds, the person loses consciousness and has no pulse. Only immediate emergency treatment, such as cardiopulmonary resuscitation (CPR) and defibrillation, can prevent death from SCA. Some patients with heart failure have a high risk of SCA.

Last updated: 20 January 2005