The effectiveness of localized retrograde coronary venous perfusion (RCVP) in preventing or reversing myocardial ischemia after acute ligation of a coronary artery is described. Ten domestic pigs (Group I) underwent aorto left anterior coronary vein grafting with RCVP at systemic pressure. In another set of ten pigs (Group II), the coronary vein was similarly grafted, but the proximal end of the graft was perfused with oxygenated blood by means of an external pump at reduced pressure and flow. In both groups, RCVP successfully reversed the mechanical or electrical effects produced by 2 to 5 minutes of acute arterial ligation. After several hours, Group I animals showed evidence of acute ischemia and developing infarction. Group II animals, however, were maintained for 7 hours or more with regional RCVP and no evidence of ischemia. Retrograde coronary venous perfusion at reduced pressure may be more effective than perfusion at systemic pressure in providing myocardial blood flow.