The myocardial capillary vasculature in repeated physical exercise. An experimental investigation in the rat

The neoformation of myocardial blood capillaries was investigated on cardiac autoradiograms from 3H-thymidine injected rats that had been swimming-exercised for two weeks, rats that had been resting for three months following the exercise, and rats in which the rest had been followed by a second two-weeks period of exercise. The initial period of exercise induced a signficant capillary neoformation in the hearts. The newly-formed vasculature was found of functional significance still at the end of the resting period and available for the increased demands on the myocardial vasculature when the exercise was resumed.