AbstractPrevious studies in patients with heart disease have shown that the stress-volume relation was linear during late ejection and that the slope of this linear portion (SLSV) could easily be determined from a measurement taken on a single cardiac cycle. The present study emphasizes, by means of a simple model, the reliability of SLSV as an index of myocardial contractility in a clinical environment. This study also indicates that SLSV is almost independent of large variations in arterial load impedance.