The religious community Jehovah's Witnesses was founded in 1870. They hold that blood transfusion is against God's law. Surgical treatment of a Jehova witness is a great challenge for every surgeon, especially for cardiac surgeons because blood transfusion is frequently needed during such operations. Authors have been trying to reduce the utilization of preserved blood for ten years. This study is about the experience with Jehovah's Witnesses who have undergone open heart surgery in Debrecen. Twenty-four patients underwent open heart surgery from 1989 till May 1999. 7 of them were males and 17 were females. The mean age was 53 years (40-70 yrs). Three patients had congenital heart disease, 11 had acquired valve disease and 7 had coronary stenosis. In 3 cases the patients had combined coronary and valve disease. Authors used a complete procedure for reducing blood loss during the operations. Two patients (8.3%) died during the early postoperative period. Preoperative mean haemoglobin level was 134.2 g/l (112-166) and haematocrit value varied between 36-50% (mean 38%). On the first postoperative day significant decrease was registrated in these values. From the second day a slow but significant increase of haemoglobin and haematocrit levels were detected. The mean follow up time was 37.6 months (2-144), and the NYHA classification of 21 longtime survivors improved from 3.06 to 1.62. At the Department of Cardiac Surgery in Debrecen as well as worldwide more and more operations are done without blood or preserved blood products, so it could be said that nowadays surgical treatment of Jehovah's Witnesses has lower risk than before.