The study was carried out in 13 mongrel dogs. Regional myocardial blood flow was measured using radiolabelled microspheres. Lactate, H+-ions, and O2 content were measured in arterial and local venous blood. Partial occlusion of the ramus circumflexus (LCX) led to a decrease in left ventricular dp/dt max, systemic arterial pressure, and a marked release of lactate from the underperfused myocardium. With DHE (2 micrograms/kg infused within 5 min, 8 dogs), a slight decrease in heart rate, left ventricular dp/dt max, LCX-resistance and a small increase in femoral and total peripheral resistance as well as in arterial and left and right atrial pressure was observed. In the normally perfused and in the underperfused part of the left ventricle microsphere assessed blood flow was unchanged or slightly elevated with DHE. Lactate release from the underperfused myocardium was markedly reduced. None of the DHE-induced effects on hemodynamic and metabolic parameters were observed in control experiments with infusion of 0.9% NaCl (5 ml). The results indicate that DHE leads to an amelioration of impaired metabolism in the underperfused myocardium and exerts no vasoconstriction in this area.