In humans with hypertension and LV hypertrophy, beneficial effects of angiotensin inhibition may be associated with preserved autoregulatory capacity. We studied the effect of acute angiotensin converting enzyme (ACE) inhibition on coronary autoregulatory pressure-flow relations and transmural distribution of blood flow in sham and LV hypertrophy dogs. Heart/body weight ratio increased (p = 0.001) from 5.5 +/- 0.7 in sham to 6.9 +/- 0.5 in LV hypertrophy dogs. The lower coronary pressure limit (LPL) on the pressure-flow relation was 47 +/- 2 mmHg in sham and 57 +/- 6 mmHg (p = 0.001) in LV hypertrophy dogs; after acute ACE-inhibition the LPL was reduced to 40 +/- 5 mmHg and 49 +/- 6 mmHg (p = 0.001), respectively. Transmural distribution of blood flow was preserved at the LPL in both groups before and after acute ACE-inhibition. Concomitant blockade of prostaglandin and nitric oxide release and bradykinin catabolism had no additional effects on the LPL and distribution of blood flow. After acute ACE-inhibition in LV hypertrophy dogs, distribution of blood flow across the LV wall was preserved and subendocardial vascular reserve was maintained even though the LPL was significantly lower. Preservation of autoregulatory capacity by ACE inhibitors contributes to beneficial outcome in patients with hypertension and LV hypertrophy.