We herein experienced 2 cases of severe tricuspid valve regurgitation (TR) and right heart failure after mitral valve surgery. In these cases, echocardiography showed a marked right ventricular dilatation and severe TR, which ware suspected to result from a right ventricular myocardial infarction at the time of the 1st operation. We considered the cause of right ventricular infarction to be an air embolism of the right coronary artery or inadequate cardioplegic perfusion to the right ventricle. Since these incidences, we have paid more careful attention to the de-airing of the left ventricle and aortic root and provided more frequent and strict delivery of antegrade and retrograde cardioplegic perfusion. Consequently, we have not since experienced any similar complications at our institute.