Eight normal subjects and 7 cyanotic patients, 5 with tetralogy of Fallot, and 2 with Eisenmenger’s syndrome, were studied with coronary sinus catheterization. In the resting state mean coronary flows were lower and myocardial oxygen extractions higher in cyanotic patients so that myocardial oxygen consumption was the same in the 2 groups. Coronary flows appeared to be inversely related to hematocrit in the cyanotic group. Myocardial lactate balance was similar in the 2 groups, but coronary sinus lactate/ pyruvate ratios were frequently higher than arterial ratios in the cyanotic group. The subjects were stressed with supine leg exercise or with an isoproterenol infusion. In cyanotic subjects exercise caused a fall in arterial oxygen and myocardial oxygen extraction so that oxygen delivery tended to be more dependent upon coronary flow. Myocardial oxygen delivery appeared adequate during stress in cyanotic patients and lactate and pyruvate analysis failed to show evidence of myocardial hypoxia. Between the 3rd and 8th min of exercise, cyanotic patients continued to have falling arterial oxygen values and rising arterial lactate and lactate/pyruvate ratios indicating that they had n
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