Coronary capillaries and cardiac myocytes constitute the principal components of the heart. The importance of the relationship between these two components is underscored by the critical role of capillaries in supplying oxygen to the working myocytes. The geometrical conditions for the diffusion of oxygen are influenced not only by the capillary density, but also by the spatial distribution of capillaries within the tissue. In the case of the subendocardium, it has long been suggested that oxygen may diffuse directly to the innermost layers of the subendocardium from the ventricular cavity, thus providing a direct, nonvascular source of oxygen to the subendocardium (Hort, 1968). Despite this longstanding idea, we are not aware of any previous studies that have considered the extent of oxygen supply from the ventricular cavity to the subendocardium. If this pathway for oxygen is appreciable, we hypothesized that this may influence the geometry of the local microvascular bed, the primary means of oxygen supply to subendocardium.