Two cases of severe haemolytic anaemia developed after heterograft valve replacement are reported. In one case haemolysis was caused by prosthetic degeneration; in the other case the heterograft was not altered, but a ventricular septal defect had created a high turbulence around the valve which was in pulmonary position. In both cases anaemia subsided after surgical correction of the abnormalities responsible for periprosthetic turbulence. Haemodialysis can only develop in patients with heterograft valve replacement if a change in blood flow rate occurs around the valve, due to its alteration or to an associated cardiac disease.