The value of esophageal phonocardiography as a noninvasive monitor during anesthesia was studied in dogs. Esophageal phonocardiograms were analyzed using fast Fourier transform and least squares linear regression technics. This method has demonstrated that it is feasible to estimate two parameters of cardiac contractility—1/(PEP)2and stroke power—and one parameter that demonstrates the state of the vasculature—total peripheral resistance. A continuous time (analog) processor that will accomplish this task is described.