Coronary occlusion before, during, and after strenuous exercise.

Groups of dogs were exercised immediately before, and immediately after occlusion of the left anterior descending coronary artery. Coronary occlusion by a staged procedure resulted in a low mortality and rare ventricular ectopic beats. The combination of simultaneous exercise with coronary occlusion reproducibly provoked ventricular fibrillation (VF). Exercise before and after occlusion frequently produced ventricular tachycardia but no VF. The risk of major arrhythmias was related to the peak heart rate resulting from the exercise.