The left ventricular (LV) pressure to volume relationships are very sensitive parameters for the evaluation of the LV function. For measurement of LV pressure in an entire cardiac cycle, an invasive method is always needed. However, on the assumption that the LV pressure is similar to that of aorta and radial artery during ejection period, we have developed a new system for simple and non-invasive assessment of the LV pressure to volume relationships. The LV volume is estimated by ECG-gated radionuclide ventriculography using a single cardiac probe system and the data were collected every 10 msec. The radial arterial pressure was measured simultaneously every 10 msec by a tonometry system. These data were transferred to the personal computer through RS-232c cable. Then the pressure to volume curves during ejection phase was generated automatically. Emax was calculated from these curves. Moreover, the new parameter called the ejection rate of change of power (ERCP) can be calculated. These parameters are very useful for the evaluation of the effect of the drugs on the LV performance.