The myocardial capillary vasculature in exercising animals with increased cardiac pressure load.

The myocardial capillary reaction was studied in normal rats subjected to swimming exercise and in rats in which aortic stenosis had been produced at various time intervals before the swimming exercise was commenced. The data obtained indicated that neoformation of myocardial capillaries during swimming exercise occurred only in rats without aortic stenosis. It is concluded that a heart subjected to an increased pressure load is less able to respond to a superimposed volume load by an increase in its capillary supply than is a normal heart.