This article describes a mathematically based human circulatory model. The model consists of lumped elements made of venous, arterial, peripheral, pulmonary vein and artery segments. A heart model is simulated using 4 chambers (left and right atriums and ventricles). The heart pump mechanism is operated by a simple piston based models for each of the chambers. The simulation consists of 19 (states) first order differential equations. and simulated with Matlab and Simulink. The simulation computes volume, flow rate and pressures in each segment.