Prolongation of the PR interval is a nonspecific condition. Etiologies include normal physiologic variance, idiopathic bundle branch fibrosis, calcific valvular heart disease, ischemic heart disease, cardiomyopathies, infections resulting in myocarditis, drugs (especially type I antidysrhythmic medications), collagen vascular diseases, tumors, trauma, electrolyte imbalances, and many other miscellaneous causes. Isolated first degrees atrioventricular block is generally not associated with an increased risk of sudden death, syncope, or progression to higher degrees of atrioventricular block. Exceptions include patients with intra-atrial conduction delays prone to atrial fibrillation, acute myocardial infarction, or bundle branch disease where higher degrees of atrioventricular block may develop. Treatment consists of correction of the underlying disorder or discontinuation of the offending medication.