We report on the case of a patient with typical clinical symptoms and ST-segment elevation in V1-V4 who was diagnosed as having acute anteroseptal myocardial infarction. Coronary angiography revealed a proximal occlusion of the right coronary artery and a patent dominant left coronary artery. After successful thrombolysis with pro-urokinase a transluminal coronary angioplasty of the right coronary artery was performed. The exact analysis of the first electrocardiogram demonstrated that the decrease of ST-segment elevation in V1-V4 should have suggested the diagnosis of right ventricular infarction. This case report demonstrates the potential hazards in distinguishing right ventricular infarction from anteroseptal infarction by electrocardiogram only.