We studied a 50 years old male patient who underwent cardiac resynchronization therapy on and off (CRT-on and CRT-off) for assessment of left ventricular (LV) function and mechanical systole synchrony using gated myocardial perfusion imaging (gMPI) and real-time three-dimensional echocardiography (RT3DE). The patient was reexamined after seven months. The comparison of these two modalities showed consistent results on assessing both the CRT-on and CRT-off conditions. This result may indicate that an immediate synchronization parameter change during CRT-on may be valuable for predicting response to CRT surgery.