The hypothesis tested was that left ventricular septal myectomy improved coexisting mitral regurgitation. The pre- and postoperative cine left ventriculograms of 39 patients were compared. The mean difference in time between studies was 15 months. Approximately one half of the patients had a reduction in mitral regurgitation. There was no association between relief of obstructive pressure gradient at rest or with provocation or symptoms and improvement in mitral regurgitation.