The aim of this study is to analyze how the End-Systolic Pressure-Volume Relationship (ESPVR) depends an ventricular volume in the diseased left ventricle. Ventricular end-systolic elastance (Emax) varies with the prevailing values of ejection pressure (ESP), end-systolic volume (ESV), and an unstressed volume term (Vo). Measurements on humans as reported in the literature are used to investigate the full range of this relationship. Our results indicate that considering Emax alone, as is usually done in clinical practice, is an insufficient approach to characterize ventricular function. Rather we propose to consider the easily attainable yet more powerful index ESV. Interestingly, ESV is also significantly correlated with the term (ESV-Vo), suggesting that ESV in itself already embodies information on this elementary index Vo.