For measurement of ventricular performance, ejection fraction (EF) has gained wide acceptance. But EF is influenced not only by changes in muscle function but also by changes in cardiac loading conditions. In case of valvular heart disease which is variable in loading conditions, EF cannot be reliable as an index of myocardial contractility. The end systolic pressure (ESP)-end systolic volume (ESV) relation, howver, is known to represent myocardial contractility, independent of changes in loading conditions. Similar results can be obtained by using peak-systolic pressure (PSP) instead of ESP. To evaluate the utility of the peak systolic pressure-end systolic volume index (PSP-ESVI) relation as an index of myocardial function, we measured $PSP&ESVI$ in 19 partents with coronary artery disease before $(PSP_1;&;ESVI_1)$ and after $(PSP_2;&;ESVI_2)$ sublingual administration of nitroglycerin. PSP was measured with standard mercury sphygmomanometer during gated blood pool scintigraphic study. ESVI was measured by count derived method after attenuation correction. $PSP_2;&;ESVI_2$ measurement was started when the fall of PSP was greater than 5 mmHg after 7-14 minutes post-administration of nitroglycerin. Mean values $({pm}S.D.)$ of $PSP_1;&;ESVI_1$ was $124.9({pm}20.7)mmHg;&;59.4({pm}39.9)ml/M^2$. Mean values $({pm}S.D)$ of $PSP_2;&;ESVI_2$, was $113.2({pm}19.9)mmHg;&;37.5({pm}26.1)ml/M^2$. There was a significant difference between mean values of $PSP_1;&;PSP_2$, (p<0.01), and mean values of $ESVI_1;&;ESVI_2$, (p<0.01). $PSP_1-PSP_2/ESV_1-ESVI_2,;PSP_1/ESVI_1$ and EF were in the range of 0.14-5.19 mmHg/ml/$M^2$, 0.67-7.68 mmHg/ml/$M^2$ and 10.8%-74.5% respectively. $PSP_1-PSP_2/ESVI_1-ESVI_2$, and EF showed exponential correlation (r=0.85, P<0.01). The correlation coefficient between $PSP_1/ESVI_1$ and EF was 0.73(p<0.01). With the above results, we suggest that $PSP_1-PSP_2/ESVI_1-ESVI_2$, and $PSP_1/ESVI_1$, can be used as an index of myocardial function.