We evaluated the adrenergic innervation of the swine and canine myocardium after placement of an Ameroid constrictor around the left circumflex coronary artery (LCX). Fluorescent histochemistry was used to identify adrenergic nerve terminals in the myocardium and coronary vasculature. Ameroid occlusion of the proximal LCX in 10 pigs for 3 wk resulted in 6 +/- 1% infarction as well as myocardial ischemia in the left circumflex region of pigs studied during exercise. However, placement of the Ameroid constrictor did not significantly alter the surface density of the nerve terminals in the LCX region of myocardium when compared with innervation of control hearts. Histological examination of the coronary arterial adrenergic innervation in Ameroid-occluded pigs revealed that coronary vessels in the circumflex region of the heart were innervated. Similarly, in seven LCX Ameroid-occluded dogs, no significant decrease in adrenergic innervation of the LCX region of myocardium was observed when compared with control dogs. In contrast LCX Ameroid-occluded pigs demonstrated significant (P less than 0.01) denervation of the left anterior descending (LAD) region of myocardium when compared with control animals. The close proximity of adrenergic nerve bundles in the proximal LAD region indicates that denervation of the myocardium supplied by the LAD may result from the dissection and/or fibrosis associated with placement of the Ameroid constrictor on the proximal LCX. Our results suggest that placement of an Ameroid constrictor on the proximal LCX does not significantly alter the adrenergic innervation of the LCX-perfused myocardium or its associated coronary vasculature. However, denervation of LAD-perfused myocardium and its vasculature may result.