BACKGROUND Myocardial hypothermia of less than 10 degrees C is an essential component of preservation of donor hearts before implantation. Here we report temperature changes and comparison of methods for maintenance of myocardial hypothermia during implantation. METHODS Twenty patients were prospectively randomized into two equal groups. In one cohort myocardial hypothermia was maintained by the "Stanford method" of continuous lavage of the pericardium and left atrium with refrigerated saline solution. In the other a cooling jacket was used without saline lavage. Temperatures at multiple sites were measured at 30-second intervals from initiation of cardiac suturing until aortic cross-clamp removal. Comparisons were made between groups at each temperature site. RESULTS The cooling jacket group temperatures were significantly lower at the left ventricular epicardium and endocardium than those of the Stanford method group. CONCLUSIONS During cardiac implantation maintenance of myocardial hypothermia with a cooling jacket resulted in significantly deeper and more consistent hypothermia of the left ventricle than pericardial and left atrial lavage with refrigerated saline solution. Blood loss from aspirated saline lavage and perfusate dilution by the saline solution were eliminated.