This study was performed to study the effects of acute pulmonary embolization (injection of autologous muscle) on global and regional (ultrasonic dimension technique) right ventricular (RV) performance, coronary hemodynamics (electromagnetic flow probes), and gas exchange during underlying critical stenosis (cuff occluder) of the right coronary artery (RCA) in eight open-chest dogs. Resting coronary blood flow (CBF) and regional myocardial performance remained unaffected by the induction of RCA stenosis. Following embolization pulmonary artery (PA) pressure, pulmonary vascular resistance, end-diastolic dimensions and pressure increased, and PA flow, stroke volume (SV), and aortic pressure (AoP) decreased (P< 0.05). There was a marked decline (60%) in CBF accompanied by severe myocardial dysfunction suggestive of ischemia (akinesis, systolic lengthening, postsystolic shortening) in the area supplied by the stenosed RCA. Gas exchange, lung compliance, andpH worsened. Release of the RCA constriction led to a fourfold increase in CBF, return of PA flow, SV, and AoP to baseline values, and disappearance of regional myocardial dysfunction despite continued pulmonary hypertension. These data indicate that RV function may deteriorate in response to even small increases in afterload if coronary vascular reserve is absent and aortic pressure is allowed to decrease.