The sensitivity of baroreceptor reflex during myocardial ischemia induced by acute occlusion of left anterior descending coronary artery (LAD) was studied in anesthetized, artificially ventilated, and thoracotomized dogs. Occlusion of LAD attenuated the baroreflex mediated changes in heart rate (HR) in response to changes in arterial pressure (AP) in the animals with intact autonomic nervous system (ANS). The HR increased significantly with the time of occlusion of LAD in control (ANS) as well as in beta-blocked group, suggesting vagal inhibition. In atropinized and vagotomized animals, the HR remained unchanged following LAD occlusion. In control group, the sensitivity of baroreflex mediated tachycardia response to hypotension and bradycardia response to hypertension, after 4 h of LAD occlusion, was reduced. In beta-blocked animals, the tachycardia response after LAD occlusion was drastically reduced to almost zero. The peak sensitivity of baroreflex bradycardia response was reduced in atropinized and vagotomized animals while the peak sensitivity of baroreflex tachycardia response increased after vagotomy. In contrast, bradycardia response was increased after beta-blockade. These data indicate that acute LAD occlusion attenuates arterial baroreflex control of HR and reduction of baroreflex sensitivity is mediated by parasympathetic efferents.