This study presents a control system model describing the functional mechanics of the controlled human left ventricle in interaction with the circulatory system and regulated by the central nervous system. The variables of the model are (i) those associated with the left ventricle, namely chamber pressure and volume, heart rate, contractility; (ii) those associated with the circulatory system, namely arterial pressure, peripheral resistance. These variables are linked by the governing equations of the system model. The parameters of the governing equations can be divided into four categories. (1) Parameters associated with baroreceptor monitoring of the arterial pressure. (2) Parameters associated with the central nervous system affecting heart rate, contractility and peripheral resistance. (3) Parameters associated with the ventricular muscle and (4) circulation bed resistance. From the system parameters certain parameters of diagnostic value are derived. To parametrically simulate the model for a subject, the subject's system is perturbed by either drug administration or mild exercise; the resulting system response (i.e. variation of the variables such as cardiac output, heart rate, etc.) of the subject is monitored. The values of the parameters of the model's governing equations are determined so as to make the model system response match the response of the subject's system. Clinical application of the model is carried out for three subjects. For each subject, the diagnostic parameters of the simulated model are obtained and therefrom physiological health states of subjects are discussed. Then, pressure perturbations (represent levels of physiological stress) are imposed on each of the subject's model systems. Therefrom, the physiological stresses are evaluated; limits to the level of stress they can safely withstand are prescribed.