Techniques are provided for performing internal measurement of heart sounds to estimate patient cardiac function in terms of stroke volume, cardiac output, or a maximum rate of change of aortic pressure with time (max dP/dt). Control parameters of the medical device are then automatically adjusted so as to optimize overall cardiac function or to provide for ventricular resynchronization therapy. In one example, heart sound signals are derived from acceleration signals received from an accelerometer. The heart sound signals are analyzed to identify S1 and S2 heart sounds as well as ejection period and isovolumic interval (ISOV). Proxies for max dP/dt, stroke volume and cardiac output are then derived from the S1 and S2 heart sounds, the ejection period and the ISOV. Alternative techniques, not requiring detection of ISOV, are employed for use if the patient has heart value regurgitation.