Cardiovascular disease is one of the main causes of death in the world. In addition, some cardiovascular diseases involve severe heart valve complications that require valve replacement. This study performed a fluid dynamics analysis for a pulsatile flow through a three-dimensional bileaflet mechanical heart valve focused on flow through the valve leaflets during systole and diastole. The blood flow exerted forces on the two leaflets in the acceleration phase until they reached their fully open position at about 0.06 sec of the cardiac cycle, accompanied by the emergence of high-energy vortical structures with fluctuations downstream of the valve. In addition, during diastole, the backflow velocity raised to about 3.6 m/s, along with high turbulent shear stresses, higher than the velocity at the peak systole. The reaction forces and stresses on the blood components can increase the risk of blood damage.