Patients who are Jehovah's Witnesses present a special problem when undergoing open heart surgery since they refuse blood transfusion. We performed 15 open heart operations for both acquired and congenital heart disease using a modified version of isovolaemic haemodilution and bloodless prime technique of extracorporeal circulation. Two patients died. One death might have been at least indirectly related to the regimen which excludes blood substitution. We believe that our experience demonstrates the feasibility of open heart procedures in Jehovah's Witnesses, although the mortality risk is increased in these patients.