The late clinical complications subsequent to cardiac valvular surgery were studied in 150 patients in a period covering from January 1976, to December 1981. Mechanical prosthesis were used in 99 patients and biological in 51. Mortality, thromboembolic events, and haemorrhages, were all considerably higher in patients submitted to mechanical than biological prosthesis, whereas the periprosthetic leaks were more often observed in cases with biological prosthesis. With regard to other complications, such as infectious endocarditis, postperfusion and postpericardiotomy syndromes, etc., as well as the surgery definitive results, appreciable differences were not found. This, we can conclude that any of all now available prosthesis, is free of complications, and the election of a particular prosthesis (mechanical or biological) must probably be individualized for each particular patient.