The purpose of this study was to determine if graft viability during simple cold storage can be monitored from alteration of myocardial electrical impedance. Six anesthetized dogs underwent rapid cardiac extirpation and were placed in simple cold storage in saline for 12 hours. Myocardial electrical impedance was measured serially by use of a LCR meter and the changes of myocardial resistivity analyzed. Myocardial specimens were taken for myocardial ATP analysis and electron microscopic study during preservation. We investigated the correlation between myocardial resistivity and myocardial ATP content. Moreover in order to predict cardiac function after simple cold storage in saline, heterotopic cardiac transplantation in the neck was performed in mongrel dogs and left ventricular Emax (LV Emax) was measured with a micromanometer and conductance catheter method. It was then investigated whether or not it is feasible to predict cardiac function of the graft afer reperfusion from the changes in myocardial resistivity. Myocardial ATP remained above 50% of preischemic value 4 hours after preservation. Ultrastructural alterations of ischemia were observed in hearts preserved for 8 and 12 hours. In heterotopic cardiac transplantation, LV Emax at 120 minutes after reperfusion recovered to 94 +/- 13% of preischemic function in 4 hour-preserved heart, 72 +/- 10% in 8 hour-preserved heart. Percent recovery of LV Emax in the former was significantly higher than that in the latter (p<0.05). Turning points from reversible conditions to irreversible ones were between 4 and 8 hours based on myocardial ATP content, cardiac function after transplantation and morphological changes. With the time of preservation, resistivity began to increase in every dog and peaked during preservation. The time required to reach the peak point of resistivity ranged from 4 to 5.5 hours. Resistivity increase rate (RIR) decreased gradually during preservation and it was over 0.1 omega cm/min until a half-life of ATP. These results suggested that measurement of myocardial electrical impedance in the preserved heart should be feasible as an indicator of graft viability during preservation in heart transplantation.