ABSTRACT: Intra‐cardiac transfusion in utero is a recent development in the treatment of erythroblastosis foetalis. As with intra‐umbilical cord transfusion, the procedure has been described as having a high risk of complication characterized by bradycardia and cardiac‐arrest. Intra‐coronary hyperkalemia was suspected as being a major contributing factor towards the complications experienced, particularly by the intra‐cardiac delivery. The procedure is warranted, however, in cases where intra‐umbilical cord transfusion is not possible. Therefore, studies comparing various methods of preparing packed cells for intravascular transfusion were initiated. The plasma potassium levels of gravity sedimented packed cells and saline washed red cells resuspended in either Ringer's lactate, pooled donor plasma or saline were measured. Products of saline washed/resuspended packed red cells transfused within 2 hours of preparation were found to have low potassium levels while exposing the fetus to minimal risk of transfusion transmitted infection and were therefore selected to be the most suitable product. Using this product, a significant decrease in the incidence of severe bradycardia resulting in cardiac‐arrest, following intravascular transfusion (32 procedures) was observed.