In our concept of the interaction between intramyocardial pressure (IMP) and myocardial perfusion, IMP is defined as the hydrostatic pressure in the soft tissue surrounding the myocardial fibers. In a mathematical model of the mechanics of the left ventricle the latter definition results in values for IMP equal to left ventricular pressure in the inner layers of the wall, and a continuous decrease across the wall to zero in the outer layers. Modulation of coronary artery flow during the cardiac cycle is predominantly due to compression of the coronary vasculature by the IMP during the systolic phase of the cardiac cycle, resulting in back-squeezing components of this flow. In a mathematical model of the dynamics of the coronary circulation, containing a large capacitance at the level of the coronary microvasculature, the modulations of coronary artery flow were found to be similar to those found in animal experiments in open-chest dogs.