Objective To evaluate left ventricular(LV)contractility and mechanical synchronization in chronic heart failure patients undergoing cardiac resynchronization therapy(CRT)before and 6 months after operation by three-dimensional speckle tracking imaging(3D-STI)and two dimensional speckle tracking imaging(2D-STI),and to compare the value of the two methods in prediction of CRT response. Methods Forty-one patients with chronic heart failure underwent CRT were involved.Three-dimensional and two-dimensional longitudinal strain(LS-3D,LS-2D)and their standard deviations of the time to peak longitudinal strain(Tls-16SD-3D,Tls-16SD-2D)were analyzed before and after CRT.Ten CRT patients and 10 healthy controls were chosen to evaluate the reproducibility of 2D and 3D STI parameters.Results At 6-month follow-up after CRT,echocardiography indices in the response group were significantly improved(all P <0.05)while only LVEF and LS-3D were improved in nonresponse group.The area under the ROC curve for LS-3D,Tls-16SD-3D and LS-2D were 0.816,0.845 and 0.661 respectively(P <0.05). The reproducibility of 3D-STI indices was superior to that of 2D-STI,especially in CRT patients. Conclusions Both 2D-STI and 3D-STI can evaluate LV myocardial contractility and the mechanical dyssynchronization,however,3D-STI is superior in prediction value and reproducibility compared with 2D-STI.