Over a period of observation of 4 years maximum, there is no significant difference between the estimated survival time (by actuarial calculation) for patients with single and for those with double prostheses. Wihin the year following operation there is not significant difference between single and double prostheses as regards: the incidence of bacterial endocarditis, of pyrexias of unknown origin, of hepatitis, of haemolytic anaemia, of bleeding complications or incidents, of coronary of peripheral ischaemic episodes, or of reduced cardiac volume. On the other hand, there is a significant difference in the incidence of neurological defects (21% for the double prosthesis group, and 5% for the single prosthesis group, p less than 0.005 and or right ventricular failure (18% and 7% respectively, p less than 0.05) in the two groups.