From September 1989 to March 1996, 13 patients with prosthetic valve thrombosis underwent reoperdtion on 16 occasions. The mean interval between implantation and reoperation was 27.8 months. The anticoagulation status was inadequate in 44% of th Instances. The majority(75%) were in NYHA functional class IV, 6 of them being in shock. Reoperation was performed for valve replacement(15 of 16 occasions) or thrombectomy(1 of 16 occasions) within 3 to 192 hours(mean 33.5 hours). Operative mortality at reoperation was 25%(4 patients). Re-thrombosis occurred In 3 patients. Long-term outcome was satisfactory in all survivors with a mean follow-up of 30.B months. The present results indicate that an early diagnosis and prompt surgical intervention is needed to decrease operative mortality.