A 61-year-old woman entered the emergency department due to worsening dyspnea. Severe mitral regurgitation was observed by transesophageal echocardiography. The patient had history of an ALCAPA (Anomalous Left Coronary Artery from Pulmonary Artery) syndrome having undergone coronary artery bypass grafting (saphenous venous graft to left anterior descending artery) 30 years before. Coronary angiography and computed tomography revealed patency of the graft, with the dilated vein running across the front of the ascending aorta and being responsible for the perfusion of the left anterior descending and circumflex arteries. To avoid injuring the patent graft, mitral valve replacement under ventricular fibrillation without aortic cross clamping was performed through a right minithoracotomy approach. Postoperative course was uneventful, and she was discharged on hospital day 7. This method appears safe, effective and useful for avoiding secondary injuries in patients with severe mitral regurgitation, previous sternotomy and patent bypass grafts.