Analysis of the pressure-dimension relationship provides a sensitive index of myocardial contractility, but widespread application of this method is limited because it requires invasive measurement techniques. The recent development of two-dimensional echocardiographic automatic boundary detection permits accurate and reproducible on-line measurement of ventricular cavity areas that can be combined with ventricular pressure measurements to derive instantaneous pressure-area relationships. In anesthetized closed-chest dogs with chronic mitral regurgitation, the slope of the ventricular pressure-area relationship was determined by obtaining baseline measurements (at baseline and after infusion of methoxamine or nitroglycerin) and measurements after infusion of a positive inotropic drug (dobutamine) alone and concurrently with methoxamine or nitroglycerin. The slope of the ventricular pressure-area relationship was altered significantly (p = 0.0002) and in the expected direction (steeper slope) from baseline to the enhanced myocardial inotropic state after dobutamine infusion. Thus on-line echocardiographic measurements of ventricular cavity area facilitate the implementation of elastance determinations to serially evaluate the myocardial contractile state under conditions of alterations in preload, afterload, and the inotropic state. This method is promising for the noninvasive evaluation of left ventricular function modified by diverse pathologic conditions.