This study compared the capabilities of 4 storage solutions in protecting the cardiac explant. Isolated rat heart was flushed with and stored in one of the storage solutions at 0-degrees-C for 7 hours. The recovery of function was assessed using the working heart perfusion. Cardiac output returned to 34 +/- 6, 59 +/- 3, 76 +/- 5, and 75 +/- 8% (mean +/- SE) of the control level in hearts stored in Euro-Collins, St. Thomas' Hospital cardioplegic, a modified University of Wisconsin (MUW) solutions, and a solution developed by us (CP-8), respectively. Therefore, MUW and CP-8 were superior to the other two solutions. During post-storage reperfusion, the coronary flow correlated directly with the aortic flow (r = 0.98), suggesting that preservation of coronary perfusion may be crucial to the recovery of function. There was also a good correlation between myocardial ATP levels and the cardiac output (r = 0.81). Thus, measurements towards the enhancement of ATP preservation and regeneration may be beneficial to the stored cardiac explant.