Interval training is theoretically attractive as a means of training the postcoronary patient, since by appropriate choice of exercise and recovery intervals substantial cardiac training can be achieved without the accumulation of anaerobic metabolities and associated increases of blood pressure and cardiac work load. Six patients with frequent exercise-induced anginal attacks coped well with a program based upon running or jogging (1/2 to 1 minute) followed by 1 to 1-1/2 minutes of slow walking. Despite a poor previous response to several months of continuous training, they showed a substantial gain of aerobic power with one year on the interval regimen. The ST segmental response to a fixed increment of pulse rate remained unimproved, but probably because of the enhanced cardiorespiratory fitness, the ST depression at a fixed work load was lessended. Twenty other patients who had also followed a continuous exercise regimen for up to one year were switched to interval-type work. Over the next year they failed to progress as fast as a group of 15 patientswho persisted with continuous effort training. While interval work is helpful to the severely disabled anginal patient, it apparently leads to slower progress in the average postcoronary patient.