1 To determine the distribution of flow, the regional haemodynamic response to 100 mg of captopril was determined in 36 patients with refractory cardiac heart failure. Measurements included forearm blood flow by venous occlusion plethysmography (eight patients), splanchnic blood flow by indocyanine green clearance (10 patients), and coronary blood flow by thermodilution (12 patients). 2 Cardiac index significantly rose in one hour (1.9 +/- 0.1 to 2.2 +/- 0.1 1/m/m2, p less than 0.01) while forearm blood flow rose slightly (2.9 +/- 0.8 to 3.2 +/- 0.3 ml/100 ml/min). Renal blood flow rose significantly by 30% (344 +/- 48 to 533 +/- 82 ml/min, p less than 0.02). Despite a fall in rate pressure product (8.8 +/- 0.7 to 7.1 +/- 0.5 mm Hg bt x 10(3), p less than 0.02), coronary blood flow did not significantly change (160 +/- 20 to 133 +/- 12 ml/min), indicating an improved supply-demand relationship. 3 External myocardial efficiency improved (19 +/- 3 to 26 +/- 6%, p less than 0.05). Coronary blood flow is unaffected and converting-enzyme inhibitor improves myocardial efficiency. This strategic reduction in vascular impedence distinguishes converting-enzyme inhibitors as a unique class of vasodilators in the treatment of coronary heart failure.