We report four cases of one leaflet immobilization which occurred early after mitral valve replacement with a Carbomedics bileaflet valve. The first case was diagnosed incidentally six days after surgery and did not require reoperation because of the spontaneous normalization of the valve movements the day before the scheduled reoperation. Since then, we have been using intraoperative transesophageal echocardiography in mitral procedures routinely (both valve repair or replacement). We were able to detect malfunctions which required reorientation in three other prostheses. We emphasize the importance of performing intraoperative transesophageal echocardiography routinely in these procedures; its high sensitivity and low risk can help to avoid a late reoperation.