Sudden cardiac death (SCD) refers to a sudden, unexpected death due to loss of heart function (sudden cardiac arrest). Sudden cardiac death is the largest natural cause of death in the United States, causing approximately 325,000 deaths among U.S. adults each year. Sudden cardiac death causes half of all heart-related deaths.

The heart muscle is responsible for circulating blood throughout the body and uses electrical signals from within the heart to manage the heartbeat. When the heart's electrical system is not working as it should, premature repolarization (ERP) can develop and cause premature repolarization syndrome.