In open heart surgery it is very important to protect the heart during the ischaemic period in terms of mortality and morbidity. Many different cardioplegic solutions are in clinical use without being tested experimentally. In this study we intended to investigate the effects of albumin addition to St. Thomas Hospital cardioplegic solution on cardiac protection to ischaemia. Rat hearts were isolated and perfused in Langendorff apparatus (n = 6 for each group). After the stabilisation period, the hearts in the control group were arrested with St. Thomas Hospital cardioplegic solution for 3 min then subjected to 30 min of global ischaemia in cardioplegic solution, this is followed by reperfusion for 10 min. In albumin groups, the experimental protocol was the same but 2.25%, 4.5% or 9% human albumin was added to the cardioplegic solution. All of the hearts were compared for their pre-ischaemic and post-ischaemic contractility, heart rate, coronary flow, LDH and CK enzyme leakage, and wet/dry weight ratio values. The contraction, heart rate (P < 0.01 for both), and coronary flow (only for the 9% albumin group, P < 0.05) values in the albumin group were less than the control group during the reperfusion period. There was no difference between groups in LDH, and CK leakage, and wet/dry weight ratio. The circulation of ischaemic hearts in the albumin group were diminished, possibly due to protein precipitation. This condition negatively affected the performance of the heart. The fact that there is no difference in enzyme leakage and wet/dry weight ratio, indicates that this event is not irreversible. (C) 1998 The Italian Pharmacological Society.