THE HEART CLINICS NEAR ME The immediate cause of sudden cardiac arrest is usually an abnormality in your heart rhythm (arrhythmia), the result of a problem with your heart's electrical system. Unlike other muscles in your body, which rely on nerve connections to receive the electrical stimulation they need to function, your heart has its own electrical stimulator — a specialized group of cells called the sinus node located in the upper right chamber (right atrium) of your heart. The sinus node generates electrical impulses that flow in an orderly manner through your heart to synchronize the heart rate and coordinate the pumping of blood from your heart to the rest of your body.