5.1 million Americans are affected by heart failure (HF). Left Ventricular Assist Devices (LVADs) are mechanical pumps attached to the heart as a HF treatment. However, LVAD patients have high risk of thrombus formation, exacerbated by altered fluid dynamics through the heart. After initial thrombus formation, thrombus growth depends on a balance of local chemical and fluid dynamic factors which we hypothesize encourages rapid thrombus growth in LVAD patients. Our aims are to measure the fluid mechanics of the LVAD-assisted heart during the development of a left ventricle (LV) thrombus using a mock circulatory loop, and to assess clinically important indices such as vortex circulation, kinetic energy, stasis, pulsatility, and residence time which can identify patients at risk for a thromboembolic event. Experiments are performed with a cardiovascular mock loop, which reproduces the cardiovascular system of a HF patient. The system is assembled with a series of silicone LV models simulating thrombus growth. The LVAD speed is gradually increased over the operational range and the velocity field is measured using Particle Image Velocimetry. The velocity is analyzed to identify the mid-plane vortices and to assess the effect of LVAD support on LV vortex formation and stasis. Fluid stasis is evaluated using the ratio of the average velocity in a region of interest located distal to the simulated thrombus to one located proximal. In the Pre-LVAD condition, the flow pattern is similar to a HF patient with dilated cardiomyopathy. Two counter rotating vortices formed from the initial transmitral jet during diastole are redirected to the LV outflow tract in systole. With low LVAD support, a portion of the flow bifurcates towards the LVAD outflow at the apex. As speed increases, LVAD flow increases until all of the flow exits the LV through the LVAD. This flow pattern results in an area of flow stasis adjacent to the LVOT, which is illustrated by a gradual decrease in the relative velocity distal to the thrombus region. The area of flow stasis is progressively worsened as the thrombus size is increased, demonstrating the positive feedback thrombus growth problems observed in some LVAD patients.