The aim of this study was to investigate coronary vascular responses, particularly NO-dependent, in the non-ischemic miocardium during local acute myocardial ischemia/reperfusion. The experiments were performed on the dogs with closed chest. Occlusion of a branch of the coronary artery resulted in a dilatation of the coronary vessels within the intact part of the myocardium. Neither inhibition of prostanoid production and KATP-channels, nor administration of atropine sulfate and dissection of the vagus nerve altered coronary dilatation within the non-ischemic myocardium. Whereas inhibition of NOS by L-NNA (50 mg/kg) completely changed it after coronary occlusion, furthemore coronary resistance temporally increased. Thus, the most reliable mechanism of that response was NO-dependent.