atrial contraction per day Premature ventricular contractions (PVCs) also account for many reports of irregular heartbeat Although this arrhythmia can herald serious underlying pathology, patients with an unremarkable history, normal physical examination, and unifocal PVCs that disappear with exercise not require further evaluation Patients with significant sinus or AV node dysfunction as a cause of an irregular or slow heartbeat often have a history of syncope or seizure, slow HR (25 to 50 beats per minute) on examination, a pulmonic flow murmur, or signs of congestive heart failure Patients who have undergone intra-atrial repairs (Dtransposition of the great arteries and atrial septal defect) are at highest risk for these potentially life-threatening arrhythmias