Since various studies suggest that chronic physical conditioning promotes myocardial vascularity, we investigated whether it could prevent the coronary reserve abnormalities of hypertensive cardiac hypertrophy. One week after operation, female Sprague-Dawley rats with two-kidney, one clip Goldblatt hypertension were either subjected to a moderate exercise program by swimming (n = 21) or kept sedentary (n = 16) for 9 weeks. Sedentary (n = 16) and exercised (n = 15) sham-operated rats served as controls. Maximal coronary blood flow and minimal coronary resistance, either per unit mass or for the entire left ventricle, an index of the functional cross-sectional area of the coronary resistance vessels, were determined in conscious, unrestrained rats by left atrial microsphere injection following maximal vasodilation with carbochrome (12 mg/kg). Following exercise, left ventricular mass was moderately (+5-10%) but significantly increased in normotensive rats, whereas left ventricular hypertrophy was significantly accentuated in the hypertensive rats. Minimal coronary resistance for the entire left ventricle was significantly decreased (-24%) in normotensive rats but did not change significantly in hypertensive rats. Minimal coronary resistance per unit mass (the coronary vasodilator reserve) tended to decrease in normotensive rats (-17%), whereas it tended to be further augmented in hypertensive rats (+13%). However, these differences were marginally significant and were not associated with any changes in maximal coronary blood flow per unit mass (the coronary flow reserve). Thus, in normal rats, exercise promoted myocardial arterial vascularity in parallel with the development of cardiac hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)