The End-Diastolic Volume (EDV) is closely related to physiological and pathological conditions in the human body.In normal physiological conditions,EDV is time-invariable.However,its variation with heartbeat usually corresponds to some pathological phenomena.N-period variation of EDV is called MP (Mechanical Periodicity).Human physiology is an overall complex nonlinear system.Nonlinear dynamics plays an important role in understanding the rhythmical and periodical phenomena of physiological nonlinear pulsation,and great success is thereby achieved.When internal and external environments change,the human blood circulation,centrally regulated by the nervous system and partially regulated by the adjacent vascular environment,can keep blood flow stable through adjusting heart rate and peripheral vascular resistance.Baroreceptors in the carotid sinus and aortic arch play an important role in regulating heart rate and peripheral resistance.In this paper,considering baroreceptor regulation of the heart rate and peripheral resistance,and using a nonlinear dynamics method,we develop a lumped-parameter homodynamic model to study the MP of EDV and to analysis the influence on it of baroreflex.