Current physiologic parameters acquired during cardiac catheterization include the systolic, minimum, and end-diastolic left ventricular pressures, the ejection fraction, and the maximum and minimum rates of pressure rise and fall. To extract additional physiologic information from the left ventricular pressure (LVP) contour, we utilized phase plane analysis (dP/dt vs P) to study LVP. One cardiac cycle generates a closed loop, or limit-cycle, in the phase plane. We hypothesized that the area of the limit-cycle is related to the external work of the heart, which is a function of both pressure and volume. We investigated the relationship between limit-cycle area (ALC) and ejection fraction (LVEF). LVP and LVEF data acquired during cardiac catheterization in ten subjects were analyzed. We observed a linear relation between ALC and LVEF with an R-value of 0.43. We conclude that new information characterizing LV function can be obtained from ALC.