BACKGROUND Because the interrelationship between the parenchymal cell population and the microvasculature is critical in normal organ function, the effects of starvation on rat myocardium were studied morphometrically with respect to the microvasculature. METHODS Morphometric analytical studies were performed on myocardium of adult, female Wistar rats (groups of 5-7 rats) on fasting days 0, 1, 2, 4, 6, 8 and 10. Since cardiac muscle is a tissue with a high level of anisotropy, methods based on the concept of vertical planes were used to describe quantitative alterations in the rat myocardium both at the cellular and ultrastructural level. RESULTS Morphometric analysis of electromicrographs of myocardium showed an increase in capillary density together with a decrease in capillary lumen cross-sectional area during starvation (p < .05). There was no significant change in volume fraction of the capillaries but surface density of the myocytes increased significantly (p < .01) and the diffusion distance for oxygen from the capillary lumen to the mitochondrion decreased (p < .01). CONCLUSIONS Malnutrition alters the interrelationship between parenchyma and vascularization in the heart. This leads to a significant decrease of the diffusion distance for metabolites. This decrease of diffusion distance may improve cellular energy supply and offers a relative protection of the metabolism in the malnourished myocyte.