Characterization of heart valve prostheses requires regurgitation tests in pulsatile flow. Although trials are often run in accordance with hemodynamic conditions of a healthy young man, heart valve implantation is often associated with other pathology, such as atrial fibrillation. To run more realistic trials, four mechanical heart valve prostheses (Björk-Shiley, Medtronic Hall, St. Jude Medical, CarboMedics) were tested with and without atrial contraction. A dual activation simulator allowed both physiological normal and pathological flows to be simulated through the mitral valve. Each valve was tested with and without atrial contraction at the same flow rate, using a solution reproducing blood viscosity conditions. Results showed the closing volume to increase significantly when comparing normal conditions with atrial fibrillation for all valves, except CarboMedics. Without atrial contraction, the valve appeared to be closed by backward flow only. This study showed that different heart valves behave differently in a pathological condition; this must be considered when choosing the valve to implant.