Purpose <p>Ventricular assist devices (VADs) are most often computationally evaluated as isolated devices subjected to idealized steady-state blood flow conditions. In clinical practice, these devices are connected to, or within, diseased pulsatile ventricles of the heart, which can dramatically affect the hemodynamics, hence hemocompatibility-related adverse events such as hemolysis, bleeding, and thrombosis. Therefore, improved simulations are needed to more realistically represent the coupling of devices to the assisted ventricle.</p> Methods <p>To address this need, we present a hybrid biophysics co-simulation strategy to evaluate the blood flow dynamics of a percutaneous catheter VAD in-situ within a pulsatile ventricle coupled to the circulation. Our hybrid strategy utilizes a computationally inexpensive lumped parameter network (LPN) to compute cardiac dynamics and provide one-way coupled physiologically-realistic boundary conditions to a high-fidelity computational fluid dynamics (CFD) model to simulate detailed hemodynamics of the VAD and the VAD-assisted left heart.</p> Results <p>Numerical simulation of a high-speed rotodynamic catheter pump configured as a left ventricular assist device (LVAD) generated a realistic reproduction of the unsteady blood velocity field over one complete cardiac cycle. The biophysics co-simulation strategy resulted in approximately one order of magnitude speed-up compared to a bidirectionally coupled CFD co-simulation. The simulated flow fields revealed persistent swirling blood flow within the ventricle, unsteady flow discharged to aorta by the pump, and significant variations of surface washing around the pump housing during the cardiac cycle.</p> Conclusions <p>This study represents a stepping stone toward physiologically and anatomically realistic evaluation of mechanical circulatory support devices that directly complements and reduces extensive in-vivo studies to mitigates risk of adverse events in the clinical setting.</p>