Is substrate supply of the myocardium limited by capillary exchange?

Data of tracer wash-out kinetics of substrates and other substances permit the calculation of myocardial capillary exchange rates. Transfer rates calculated from these data and from known plasms substrate concentrations are close to the extraction rates observed by several authors. The substrate pattern offered for the myocardial cell, calculated from the capillary transfer, is also very similar to that extracted. These findings indicate that myocardial substrate consumption is determined and, under certain circumstances, even limited by capillary exchange. Limitation of capillary substrate transfer might act as a bottleneck of myocardial energy metabolism and might induce myocardial cell necrosis under certain conditions.