Cardiac motion related artifact in ultrasound induced thermal strain imaging (TSI) was reduced in-vitro and in-vivo using ECG gating. Tissue motion due to the heart beat is a major challenge for in-vivo TSI application, especially for cardiovascular systems. Temporal variation of the relative position between the transducer and the artery will induce decorrelation in speckle tracking. Tissue deformation produces mechanical strains directly. Thermal strains are equivalent to their motion-induced mechanical counterparts and are typically an order of magnitude smaller. Consequently, effective reduction of motion artifacts is critical for clinical use of TSL Using ECG signals to trigger array firing, cardiac periodicity can be fully utilized to minimize motion artifacts, allowing thermal strains to accumulate over multiple cardiac cycles with little distortion. TSI gated by the lumen pressure signal on an artery phantom (rubber) connected to a pulsatile pumping system compares well with TSI when the phantom was immobile for the same heating/imaging sequences. An in-vivo test was performed on a rabbit femoral artery under local animal protocol. The animal's ECG gated a similar pulse sequence used for the phantom. The in-vivo temperature rise in the femoral arterial wall was also estimated. This estimation is well above the background noise in TSI due to speckle tracking error or/and any possible residual vibration. Breathing motion artifacts can be minimzed in the clinic through a breath hold.