Coronary blood flow was measured by the nitrous oxide method, and cardiac output was measured by the Fick principle, in a series of 31 human subjects with the clinical diagnosis of angina pectoris. Coronary arteriography was carried out on the same subjects as a part of the same procedure, and the extent and severity of the coronary artery lesions was determined. A numerical value was assigned to the severity of the coronary artery disease, an attempt was made to correlate the severity of coronary artery disease with the measured coronary blood flow and with various hemodynamic parameters which traditionally describe the systemic and pulmonary circulation. There was no correlation between any of the parameters measured and the severity of coronary artery disease demonstrated by angiography. It is concluded, therefore, that the nitrous oxide method for measuring coronary blood flow is not helpful in separating subjects with normal coronary arteries from those with coronary artery disease, nor are resting hemodynamic observations helpful.Maximum flow through the coronary arteries of the dog heart was measured by postmortem perfusion. This flow rate is sufficient to provide a considerable factor of safety as far as constriction of the major coronary arteries is concerned. If these data are extrapolated to the coronary vessels of man, it would seem that a very large "safety factor" exists, and this may explain why severe coronary disease is not revealed by studies of coronary blood flow. Additional Indexing Words: Myocardial metabolismCardiac cathet A LTHOUGH many reports are available on the determination of myocardial blood flow by the nitrous oxide method in subjects prone to have angina pectoris,'-8 there are few in which the coronary arteries were studied by angiography. We have found no study in which an attempt has been made to correlate the severity of coronary artery disease as demonstrated by coronary arteriography with coronary flow as determined by the nitrous oxide method, although some ob-

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Twelve subjects with an average age of 65.9 years who had complete heart block had cardiac output and coronary blood flow measured at three different rates of pacing. Cardiac output and calculated external work increased with rate from the slow to the intermediate rate, but declined at the fast rate. Even at the intermediate rate, cardiac output remained low as compared to standards for normal younger subjects. Coronary blood flow and left ventricular oxygen usage increased with cardiac rate. Cardiac efficiency, expressed as left ventricular work divided by left ventricular oxygen consumption, tended to decrease as cardiac rate rose; however, these changes were not statistically significant. Lactate consumption increased with rate, but changes in glucose and pyruvate consumption were not significant. Considering the eirculatory svstem as a whole, the intermediate or normal resting rate was more efficient. At this rate the cardiac output and cardiac work were greatest, and the mixed venous oxygen content (which must reflect body tissue oxygenation) was highest, wlile the cardiac oxygen] consumption and coronary blood flow were intermediate.

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