Effects of age and exercise on the extent of the myocardial capillary bed

The age‐related response of the ventricular capillary bed to enhanced work loads was investigated in male albino rats. During the 12‐week experimental period young, adult and old animals were trained on a motor‐driven treadmill. Resting bradycardia was found to occur after 8–12 weeks of training. Demonstration of the ventricular capillary bed was accomplished by injecting Pelikan biological ink retrograde into the ascending aorta of a beating heart. Capillary/muscle fiber ratios were slightly (6.5–9.5% ), but significantly, increased in all trained groups. The number of capillaries/mm 2 decreased with age but was higher in trained animals. Thus while aging is associated with a decrease in the concentration of ventricular capillaries, chronic exercise provides some mechanism which enhances the extent of the capillary bed.