One of the major challenges in perfusing an explanted human heart is gaining access to human blood. A pure crystalloid perfusate (CP) apparatus was implemented to circumvent this problem. To test the efficacy of the system, we compared the electrophysiology (EP) before [in vivo (IV)] and after [ex vivo (EV)] heart excision (275±32 g) in 6 pigs. Endocardial unipolar electrograms and monophasic action potential (MAP) signais were recorded at the LV apex during sinus rhythm and at pacing cycle lengths (PCL) of 400, 350, 300, and 250 ms IV and at 1 (EV-1) and 2 (EV-2) hours after perfusion was initiated. The MAP duration at 90% repolarization (MAPD90) was determined at each PCL. Effective refractory periods (ERP) were determined at LV endocardium in IV and at EV-1 and EV-2. Results: MAPD90 decreased monotonically as the PCL decreased from 400 to 250 ms during IV and EV portions of the study. Differences between IV, EV-1, and EV-2 were not .significant at each PCL. The LV ERP at EV-1 (234±33 ms) was not different from IV (218±10 ms) and EV-2 (235±11 ms). However, the ERP at EV-2 was longer than IV (p<0.05). Conclusion: These preliminary data suggest that EV perfusion of swine hearts can be performed for short periods of time (1-2 hours) with a CP without dramatically altering cardiac EP. It may be a possible viable alternative in explanted human heart studies.