This study developed methods for imaging left-ventricular (LV) mechanical activation, with application to identifying optimal LV pacing sites for cardiac resynchronization therapy (CRT). Cine displacement encoding with stimulated echoes (DENSE) was used for strain imaging, and mechanical activation time was defined as the time of onset of circumferential shortening (TOS). Active contours were applied to strain data to automatically compute TOS. Results showed a strong correlation between TOS and electrical activation time, heterogeneity of the location of latest activation, and a significant association between TOS at the LV pacing site and CRT response. These methods may enable improved CRT implementation.