Variations in electrocardiographic responses during exercise; studies of normal subjects under unusual stresses and of patients with cardiopulmonary diseases.

T HE CHANGES of the Q-T interval during and after exercise in normal subjects, and in patients with cardiopulmonary diseases, have been described in a previous communication.' Level walking was done on a motor driven treadmill for 10 minutes, or less if markedly disabled, at a pace of either 1.73 or 2.60 miles per hour. In normal subjects the corrected Q-T interval was prolonged during exercise, shortened during early recovery and then returned to resting value during late recovery. The Q-T: T-Q ratio increased about 40 per cent during exercise and it returned promptly (to resting value) during early recovery. There were no significant changes in the RS-T segment or T wave. In patients with cardiopulmonary diseases, the changes in the Q-T interval showed somewhat different patterns. The frequency of abnormal response in the Q-T interval varied inversely