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SUMMARYThe coronary flow must increase if elevated myocardial oxygen demands are to be met adequately. This increased flow is achieved through coronary artery dilatation (autoregulation) but can reach the subendocardial region only during diastole (intramyocardial compressive forces are greatest in the subendocardium and therefore prevent its perfusion during cardiac contraction).4-7 When subendocardial vessels become maximally dilated, subendocardial flow will be determined by the coronary driving pressure (coronary artery diastolic pressure minus the opposition to flow offered by diastolic intramyocardial compressive forces or coronary sinus pressure) and the duration of diastole. In the absence of coronary artery obstruction, these factors are represented by the area between the aortic and left ventricular pressure curves in diastole. We have referred to this area as the diastolic pressure time index (DPTI).8While DPTI indicates potential subendocardial blood supply, the adequacy of this supply is determined by how well it meets simultaneous oxygen demands. We estimated myocardial oxygen demands

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