The clinical importance of myocardial ischemia without associated symptoms in patients with atherosclerotic coronary disease has not been clarified. We present three patients in whom painless cardiac ischemia was associated with the induction of cardiac arrest and/or ventricular tachycardia/fibrillation. In the two surviving patients, programmed ventricular stimulation did not induce ventricular arrhythmias. In one patient, successful coronary bypass surgery resulted in the elimination of exercise-induced painless myocardial ischemia and associated ventricular fibrillation; the other patient suffered a myocardial infarction after which ischemia and ventricular tachyarrhythmias could not be reproduced with exercise testing. We conclude that painless myocardial ischemia can cause life-threatening arrhythmias and is, therefore, a potentially lethal phenomenon.