As the number of patients undergoing cardiac valve replacement has grown, valve reoperations have become increasingly frequent. The newer generations of mechanical valves are far more efficient and freer from structural failure than the older ones. However, other valve and non-valve related complications still constitute a major cause of morbidity and mortality. On the other hand, bioprostheses, implanted in large numbers in the 1970's and early 1980's, have now gone into the second decade of life since implantation, when biodegradation becomes more frequent. Reoperations are technically more demanding than the original valve procedures because of the mediastinal and pericardial adhesions and the condition of the anulus after removal of the previous prosthesis. Greater awareness of the most dangerous steps and refinements to surgical technique have contributed to the decreased mortality observed in recent years. The risk is higher in certain conditions, such as the presence of prosthetic valve endocarditis and the patient being operated on an emergency basis in NYHA functional class IV. It may also be increased in females and the elderly. Multiple reoperations also carry a higher risk in most surgeon's experience. However, elective reoperations for defective mechanical valves and for replacement of a previously repaired mitral valve carry similar mortality rates to primary valve replacement procedures. The global mortality rates have not been significantly higher in the hands of experienced surgeons working in centers where reoperations are performed frequently. In smaller series high mortality rates are a constant, which underscores the importance of the learning curve. The indications for reoperation must therefore consider all risk factors and, when possible, the procedure must be performed by those who have the most experience. Under these circumstances, elective re-replacement of degenerating bioprostheses and of defective mechanical valves in asymptomatic patients may be advisable.