Except for the electrocardiogram objective evaluation of the functional state of the coronary circulation in man is often difficult. The nature of the coronary circulation in the presence of known coronary insufficiency has not been evaluated. In this report, 17 patients were studied of whom 14 had angina pectoris. Observations were made of coronary blood flow and hemodynamics both at rest and following administration of nitroglycerin. The authors conclude that resting coronary flow is normal, but cannot increase further with dilators. They consider this phenomenon a consequence of prior exhaustion of the dilator capacity of the arterioles in compensation for the atherosclerotic obstruction of the coronary tree. The "fixed flow" concept is suggested as an objective means of detecting coronary insufficiency. Nitrites probably relieve pain in some manner other than general coronary dilatation.U NTIL the present time few objective assessments' of the state of the coronary ('irculatioll have been made except for electrocardiographic and ballistocardiographic observations. In these studies correlation was possible only with clinical findings and postmortem observations. The electrocardiogram has been extremely helpful, particularly when it has indicated myocardial isehemia. As has been pointed out by many workers, however, it gives only indirect information concerning the state and adequacy of the coronary eiren-

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