The University of Wisconsin solution, which contains the impermeant lactobionate and has an intracellular-type electrolyte composition, has been shown to improve donor heart preservation. Because a deleterious effect of the intracellular-type solutions has been reported, we evaluated a new lactobionate-based extracellular-type solution, by comparing it with University of Wisconsin solution and a crystalloid cardioplegic solution in 45 rabbit hearts. Hearts were arrested by infusion of these solutions and immersed in the same solution (lactobionate-based extracellular-type solution, University of Wisconsin solution) or in the lactated Ringer's solution (crystalloid cardioplegic solution) for 6 hours at 4 degrees C. A Langendorff circuit was used for reperfusion. Left ventricular compliance was better preserved with both lactobionate-based solutions than with the crystalloid cardioplegic solution. Adenosine triphosphate was best preserved with the lactobionate-based extracellular-type solution after arrest and after reperfusion, whereas reperfusion arrhythmias were less marked with the University of Wisconsin solution. These results suggest that lactobionate plays an important role in the preservation of ventricular compliance and that the lactobionate-based extracellular-type solution is preferable for adenosine triphosphate preservation. Further study will be required to assess the factors predisposing to reperfusion arrhythmias.