Objectives: To examine the reliability of the QRS amplitude of the autonomous intramyocardial electrogram (IMEG) and the maximum slope of the descending T wave (Tslew) of the ventricular evoked response (VER) for surveillance of acute allograft rejection (AR) after heart transplantation in rats. Methods: Forty rats underwent heterotopic heart transplantation, including ten isograft (isograft group) and 30 allograft (allograft group) recipients. Autonomous IMEG and VER were recorded with epicardiac pacing leads. Isograft recipients were sacrificed on postoperative day 7 and allograft recipients on postoperative days 3, 5 and 7. Graft heart histopathological examinations were performed at the corresponding time points. Results: Postoperative QRS amplitude and Tslew gradually decreased in the allograft group, but were unaltered in the isograft group. Decreases in the allograft group QRS amplitudes and Tslew values correlated with the histopathological results. At the optimal cutoff point of 90%, Tslew had 94.74% sensitivity, 81.82% specificity, 82.61% positive and 90% negative predictive values. QRS had 68.42% sensitivity, 90.91% specificity, 92.86% positive and 62.50% negative predictive values at its optimal cutoff point of 72.3%. Conclusions: The QRS amplitude of the autonomous IMEG and Tslew of VER are reliable markers for monitoring AR after heart transplantation in rats.