Increased QT and QT dispersion has been linked to arrhythmic death in patients with congenital and acquired long QT syndromes. The repolarization abnormalities were studied in 45 patients with a history of chest pain, somnolence, or disorientation admitted to the hospital for cocaine abuse. Group I was composed of patients with anginal chest pain (n = 23), whereas in group II patients (n = 22), chest pain was absent. Measurements were made of QT and QTc and of QT and QTc dispersion characteristics. Cocaine prolonged the QT, QTc, and QTc dispersion and enhanced the appearance of abnormal U waves. Lethal ventricular arrhythmias were observed in 3 patients. Anginal chest pain may be a marker for myocardial ischemia and, in the presence of abnormal ventricular repolarization, may cause lethal ventricular arrhythmias and sudden death in persons exposed to cocaine.