The microcirculation of the human heart: end-capillary loops with discrete perfusion fields.

We studied 10 autopsied human hearts by perfusing colored Microfil into separate coronary arteries to define organization of capillaries at the borders between two perfusion fields. Sections of "cleared" myocardium were examined with epiillumination at the grossly identified borders of Microfil perfusion. In two- and three-color-injected hearts, the capillaries were arrayed in a pattern of arcades and loops without connections between separately perfused capillary beds. In hearts perfused through only one coronary artery, the capillaries were organized into tufted loops at the border. These findings contrast with the microcirculatory pattern in canine skeletal muscle and brain, in which heterologous capillaries are focally interconnected. We conclude that the human microcirculation is composed of end-capillary loops that supply discrete perfusion fields. This pattern of unconnected heterologous capillary beds suggest that there is no obvious anatomic arrangement of the microcirculation that could account for a significant ischemic lateral border zone in human myocardial infarctions.