Extensive cryoablation of an arrhythmogenic left ventricular posterior papillary muscle associated with ventricular arrhythmias may affect mitral valve function. We studied the long-term effects of extensive cryoablation of the posterior papillary muscle and its ventricular attachment in 10 dogs. The dogs had hemodynamic, electrophysiological, and angiographic testing 1 month after operation. Seven dogs were then killed, and the hearts were examined at that time. Three dogs had repeat assessments 2 and 3 months after operation before they were killed. At 1 month, left ventricular angiography showed normal mitral valve function in all dogs. Pathological examination revealed that the posterior papillary muscle and its left ventricular attachment were replaced by a discrete dense, fibrous scar. The fibrous process involved the mitral valve in 2 dogs. At 3 months, pathological examination showed a marked fibrous scar with chondroid metaplasia and fibrous involvement of the mitral valve chordae and posterior leaflet in all 3 dogs. We conclude that extensive cryoablation of the posterior papillary muscle is not associated with long-term mitral valve dysfunction, and may be the best surgical technique to ablate an arrhythmogenic papillary muscle.