Malfunction of a St. Jude medical heart valve in mitral position.

Early postoperative intermittent malfunction in a St. Jude mitral valve prosthesis is described. The patient underwent reoperation and had an uneventful recovery. After explantation, the prosthesis underwent laboratory examination. The findings included a minimal disproportion between leaflets and valve ring causing intermittent inhibition of leaflet motion. The unpredictable irregularity of the malfunction phenomenon in vivo, confirmed by laboratory investigations, is explained as a result of a changing myocardial tension status sufficient to alter the ring to leaflet proportion of the valve in either direction.