Alteration of ischemic cardiac function in normal heart by daily exercise.

Myocardial function, tissue blood flow, and heart rate measurements were studied during control and a 2-min occlusion of the left circumflex coronary artery in conscious dogs. These measurements were made in the same dogs before exercise in the untrained state (UT) and after a 4-wk treadmill exercise program in the partially trained condition (PT). Ultrasonic segment length gauges were used to measure myocardial function in the ischemic zone, defined by staining the myocardial tissue. Microspheres (15 microns), labeled with different isotopes, were used to measure the myocardial tissue flow in the normal and ischemic zones. Myocardial function in the ischemic zone of 20 dogs was reduced 71 +/- 6% in the UT condition; however, after PT, the percent reduction in segment length function was only 33 +/- 4% during occlusion. During occlusion, an increase in heart rate of 46 +/- 7% in the UT condition was observed; yet after PT, heart rate increased only 19 +/- 5%. In 5 UT dogs with heart rate held constant (150 beats/min), the decrease from control in tissue blood flow to the ischemic zone in the subendocardium during occlusion was 60 +/- 7%. After PT, the decrease from control in tissue blood flow in the same dogs was 34 +/- 6%. These data indicate that the improved myocardial function during ischemia was a result of the improved coronary collateral blood flow into the ischemic zone after PT.