Subaortic stenosis caused by anomalous papillary muscle of the mitral valve.

We report on a rare case of subaortic stenosis caused by an anomalous posteromedial papillary muscle inserting directly into the anterior mitral leaflet, which had muscular extension to the subaortic region. Resection of the muscular extension alone was ineffective. A second operation including entire resection of the anomalous papillary muscle and mitral valve replacement resulted in successful relief of the obstruction. Microscopic findings of the resected tissue were compatible with those of hypertrophic cardiomyopathy.