BACKGROUND Automated echocardiographic measures of left ventricular (LV) cavity area are closely correlated with changes in volume and can be coupled with LV pressure to construct pressure-area loops in real time. The objective was to rapidly estimate LV contractility from the end-systolic relations of cavity area (as a surrogate for LV volume) and femoral arterial pressure (as a surrogate for LV pressure) in patients undergoing cardiac surgery. METHODS Studies were attempted on 18 consecutive patients with recordings of LV pressure, LV area, and femoral arterial pressure on a computer workstation interfaced with the ultrasound system. End-systolic pressure-area relations (in terms of pressure-area elastance [E'es]) from pressure-area loops during inferior vena caval occlusions were determined before and immediately after cardiopulmonary bypass using both LV and arterial pressure by semiautomated and automated iterative linear regression methods. RESULTS Data sets were available for 13 patients before and 8 patients after bypass (21 studies in 14 patients). E'es by arterial pressure was closely correlated with E'es by LV pressure: r = 0.96, standard error of the estimate = 2 mmHg/cm2, y = 1.01 x -0.7 by the semiautomated method and r = 0.94, standard error of the estimate = 3 mmHg/cm2, y = 1.02 x -0.5 by the automated method. Analysis of semiautomated and automated estimates of E'es from arterial pressure and E'es using LV pressure by the Bland-Altman method showed no systematic measurement bias and calculated limits of agreement of 8 and 9 mmHg/cm2, respectively. Similar decreases in E'es by arterial and LV pressure occurred from before to after bypass in 7 patients with paired data sets: 32 +/- 12 to 15 +/- 6 mmHg/cm2 and 32 +/- 15 to 15 +/- 7 mmHg/cm2, respectively (P < 0.05 for both). CONCLUSIONS On-line femoral arterial pressure and LV area data by echocardiographic automated border detection may be used to rapidly calculate E'es as a means to estimate LV contractility in selected patients.