Recent work has shown that UW may be better than standard cardioplegic solutions for short-term heart preservation. In this study we have used a rabbit heart model to evaluate a simplified UW solution in which penicillin, dexamethasone, insulin, allopurinol, and adenosine were omitted and 5% polyethylene glycol (PEG20M) was substituted for hydroxyethyl starch. The test systems consisted of 4-hr cardioplegic storage at 15°C with repeated flushing every 30 min for 2 hr and 24-hr hypoxic low-flow microperfusion (3 ml/g/24 hr) at 0°C. Control groups were arrested with a 15–25 ml flush in iced saline and immediately tested. Cardiac output (CO)* after preservation was measured in a working heart model using an acellular perfusate at 37°C at an aortic pressure of 100 cm H2O. The CO (ml/g heart wt/min) were as follows—Controls: St. Thomas II 20.5± 8.3 (5), UW 34.7±11.7 (16), PEG20M 41.8±4.4 (14); 4-hr cardioplegia: St. Thomas II 17.4±0.9 (4), Bret-schneider HTK 14.9±7.0 (4), UW 25.2±11.5 (9), PEG20M 41.1±7.8 (8); 24-hr microperfusion: UW 25.4±11.1 (18), PEG20M 37.1±8.2 (18). Following cardioplegic or microperfusion preservation, PEG20M hearts functioned at control levels (P>0.05) and were significantly superior to all other solutions, with approximately double the CO (P<0.05, all other groups). We conclude that for heart preservation, 5 components can be eliminated from UW and substitution of PEG20M for HES appears to have improved its performance.