Abstract: Pulse contour method for the determination of cardiac output are attractive because it operates on a beat-to-beat, continuous non-invasive, safe basis and can be made automatic and inexpensive. In this paper we describe how the model of cardiovascular system leads to a formulation of cardiac output with pulse contour parameter as the calibrator. This formula shows that the cardiac output is directly proportional to the difference between systolic pressure and diastolic pressure and inversely proportional to the square of pulse contour parameter K. So it is of great use in clinic practice and clinic results are satisfactory.