BEST HEART DOCTORS NEAR ME What is the main cause of cardiac arrest? Sudden Cardiac Arrest Symptoms and Causes The main cause of cardiac arrest is often a severe irregular heart rhythm, particularly ventricular fibrillation, which is a rapid, chaotic quivering of the heart's lower chambers instead of proper pumping. This electrical malfunction is usually caused by an underlying coronary artery disease (blocked arteries) or other heart conditions like a scarred or thickened heart muscle, which make the heart more prone to dangerous arrhythmias.