Acute allograft rejection is a major cause of morbidity and mortality following heart transplantation. There is no reliable noninvasive test to diagnose rejection. We aimed to investigate the accuracy of strain by speckle tracking echocardiography in the detection of acute rejection. We identified acute rejection episodes in patients followed at a single transplant center. Data were collected at baseline, during rejection and two follow-up points. Peak systolic radial and circumferential strain at the level of papillary muscles and peak systolic longitudinal strain from apical four-chamber view were analyzed offline. ANOVA was used for comparison between groups. p value ≤0.05 was considered significant. Fifteen rejection episodes were identified. There were no differences in the fractional shortening, LV posterior wall thickness, E/A, septal E/E', septal S', lateral E/E', lateral S', or MPI during rejection, compared to baseline. There was a significant increase in the LV mass during a rejection episode (47.5 vs. 34.4 g/ht(2.7) [p = 0.03]). The peak systolic radial strain (18.3 vs. 26.5; p = 0.03), longitudinal strain (-11.7 vs. -14.6; p = 0.05), and circumferential strain (-14.4 vs. -21.7; p = 0.05) declined significantly during rejection. In conclusion, peak systolic radial, longitudinal and circumferential strain decline and LV mass increases during an episode of rejection.