Healthy heart valves act as gateways to ensure unidirectional blood flow inside the normal heart. Dysfunctional valves compromise cardiac output and disrupt the intraventricular flow pattern, resulting in a degeneration of cardiac function. In the presence of a left ventricular assist device (LVAD), valvular dysfunction can significantly affect patient outcomes. As LVAD implants become more common, the duration of LVAD support routinely exceeds several years. Flow-related complications such as stroke, thromboembolism, and valve dysfunction worsen, indicating that subtleties of flow architecture are increasingly important. The LVAD patient population is challenging to study as numbers are few, and many have co-morbidities. Furthermore, flow measurement in LVAD patients relies on Doppler echocardiography, which does not produce high-quality velocity measurements. To overcome these challenges, a mock circulatory loop was developed to mimic the hemodynamics of end-stage heart failure (HF) and study the flow interaction of heart valve dysfunction and LVAD support. Aortic insufficiency (AI) is a serious complication in >20% of LVAD patients within one year post-implant. Pre-existing mild AI is often untreated but can rapidly progress to significant AI that requires repair. Hemodynamics and intraventricular flow were measured for three levels of LVAD support combined with three levels of AI severity in the mock loop. LVAD support worsened regurgitant flow for all AI levels, creating a recirculating flow in the ascending aorta. Conventional indices were not sensitive to these increases, but our results suggest alternative indices such as aortic valve net flow and energy dissipation rate may be more effective for AI assessment in LVAD patients. Dysfunctional mitral valves are also common in advanced HF patients and may be repaired or replaced by mechanical or bioprosthetic valves. Each design produces a unique inflow pattern that affects LV vortex formation and residence time. When combined with LVAD support, the best flow conditions were observed with the bioprosthesis. Valve dysfunction, whether aortic or mitral, disrupts the intraventricular flow and contributes to declining heart function. When combined with the mechanical alterations imposed by a LVAD, the flow interactions become of great clinical importance for assessing the progression and associated risk of thrombus, stroke, and AI.