Modified Euro-Collins solution (ECS), which has been successfully used in kidney, liver and lung transplantation, was tested concerning myocardial and endothelial preservation in nine piglets. In six (group I), 1-hour cardiac arrest was induced with cold modified ECS, and in three (group II) heart-lung transplantation was performed, using modified ECS for graft preservation. In group I myocardial energy preservation was determined with biochemical assays for adenosine triphosphate, creatine phosphate, lactate and creatine 5, 15, 30 and 60 minutes after aortic clamping, and preservation of endothelium in the aorta and coronary arteries was studied with scanning electron microscopy. In group II electron microscopy was performed on endothelial samples from the ascending aorta and coronary and pulmonary arteries of the heart-lung block after excision, after 2 hours of ischemia, and after 1-2 hours of reperfusion. High-energy phosphates decreased progressively during the ECS cardioplegia in group I, and circulatory support was required during the post-transplantation reperfusion period in group II. The endothelial lining in all specimens was remarkably well preserved, however. Modified ECS flush thus was ideal for vascular endothelium but, because of its poor energy-preserving capacity, unsuitable for cardioplegia.