To evaluate consequences of cardiac beta-2 adrenoceptor stimulation on coronary hemodynamics and regional myocardial function assessed by sonomicrometry in the normal and regionally ischemic heart, the effects of administration of procaterol, a selective beta-2 adrenoceptor agonist, into the left circumflex coronary artery (LCX) were examined in the absence and presence of a stenosis of the LCX in anesthetized open-chest dogs. The stenosis of the LCX was made sufficient to decrease percent segment shortening in the LCX-perfused region to around 2 to 3%. When coronary stenosis was absent, intracoronary infusion of procaterol (6.7 ng/min for 15 min) produced significant increases in LCX flow and myocardial segment shortening in the infused region without changes in global hemodynamics. During coronary stenosis, on the contrary, intracoronary procaterol at the same dose significantly deteriorated regional myocardial dysfunction without changing LCX flow, global hemodynamics and cardiac lactate metabolism. These changes induced by procaterol were not observed in the dogs treated with a selective beta-2 antagonist, erythro-(+/-)-1-(7-methylindan-4-yloxy)-3-isopropylaminob utan-2-ol. These results suggest the presence of functional beta-2 adrenoceptors in the canine heart both with and without myocardial ischemia.