Despite the routine use of right ventricle (RV) pacemakers to treat sinus node dysfunction, atrioventricular (AV) block, and other electrical abnormalities in the heart, recent studies have demonstrated that chronically RV-paced patients have an increased the risk of hospitalization, heart failure (HF), and death. Dyssynchronous electrical and mechanical activation of the left ventricle (LV) has been demonstrated in animal models of acute RV pacing. In humans, acute and chronic RV pacing have been demonstrated to impair LV systolic function and induce longitudinal or radial mechanical dyssynchrony. However, the 3-dimensional LV mechanics that result from acute and chronic RV pacing have not been fully explained. Recent advances in echocardiographic image analysis, including tissue Doppler imaging (TDI) and speckle tracking echocardiography (STE), can quantify LV motion in multiple planes throughout the LV. This dissertation will examine the effects of RV pacing on LV mechanics and synchrony in longitudinal, radial, and rotational planes of motion. We hypothesize that acute RV pacing will result in reduced and dyssynchronous longitudinal, radial and rotational LV function. We further hypothesize that these alterations to normal LV function may lead to HF during chronic RV pacing, and that this type of HF is structurally and functionally different than HF due to other causes. These results may provide insight into the mechanisms responsible for pacing-induced LV dysfunction, and enable physicians to better track cardiac function in paced patients, and modify treatments or design new therapies for patients requiring ventricular pacing.