Experimental study of mitral valve incompetence and mitral valve lesions following papillary muscle inactivation in the dog

The effect of papillary muscle inactivation on mitral valve competence has been studied in 28 dogs for up to six months. Ten animals showed evidence of mitral incompetence at some stage. In only two was severe incompetence produced, and one of these animals died after 20 days. In five of the 10 animals mitral incompetence regressed in the follow-up period. Fibrotic or calcific lesions were found in the mitral valves of five animals, but in only three were these gross.