A 55-year-old man was admitted to our department with a diagnosis of acute inferior myocardial infarction; 1 week later he underwent percutaneous transluminal coronary angioplasty on the proximal right coronary artery; during this procedure, the patient experienced chest pain and his electrocardiogram showed ST-segment elevation in the anterior leads; ventricular fibrillation also occurred. The ST-segment abnormality disappeared within 45 min, and no stenosis or spasm on the left coronary artery were detected during angiographic control; the blood flow in the right coronary artery was normal, but the acute marginal branch was occluded. This is a rare case of right ventricular ischemia caused by occlusion of the acute marginal branch during coronary angioplasty on the right coronary artery.