Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via (traveling through) an abnormal electrical pathway through the heart. Ventricular fibrillation (VF) is a potentially fatal change of the heart’s rhythm where the ventricles (lower chambers of the heart) merely quiver and do not contract in a coordinated way. No blood is pumped from the heart during VF, so it is a form of cardiac arrest (heart attack). Which of the following is the most common cause of ventricular fibrillation?