The purpose of this study was to investigate the relationship between the left ventriculo-arterial coupling and the left ventricular (LV) mechanical efficiency in human hearts with acute myocardial infarction (AMI) after thrombolytic therapy combined with subsequent percutaneous coronary intervention. Twenty-six patients with post-AMI at cardiac catheterization were divided into two groups according to their resting ejection fraction (EF). The first group included 18 patients with EF greater than or equal to 50%, and the second group consisted of 8 patients with EF less than 50%. LV pressure-volume relations were measured by the conductance catheter method with preload altered by inferior vena cava obstruction in the 26 patients who received the thrombolytic therapy in 6 h and the percutaneous coronary intervention at first week after the AMI event. The ventriculo-arterial coupling relationship was determined by the ratio of the ventricular chamber elastance Ees (the slope of the LV end-systolic pressure relation) and the effective arterial elastance Ea (the slope of the arterial end-systolic pressure-stroke volume relation). The results showed no significant difference in the ratio of Ees/Ea between Group 1 (0.78 ± 0.34) and Group 2 (0.72 ± 0.22). Significant difference (p < 0.05) in the stroke work was found between Group 1 (7188 ± 1923 mmHg × ml) and Group 2 (5677 ± 670 mmHg × ml), although the potential energy in Group 1 was not significantly different from that in Group 2. We also found in the two patient groups that Ees but not Ea was linearly increased with the Ees/Ea ratio (Group 1: r = 0.84, p < 0.001 and Group 2: r = 0.76, p < 0.05). In addition, the ventricular mechanical efficiency in the infracted hearts with EF more than 50% (r = 0.71) was shown to be linearly increased with the Ees/Ea ratio, but not in those with EF of less than 50%. We concluded that in spite of no significant difference in the values of Ees/Ea between the infarct hearts with larger EF and those with smaller EF, all infarcted LV elastance but not their afterload depends linearly on Ees/Ea. Also, in myocardial infarcted patients with higher EF, their † Biomed. Eng. Appl. Basis Commun. 2008.20:223-230. Downloaded from www.worldscientific.com by NANYANG TECHNOLOGICAL UNIVERSITY on 08/25/15. For personal use only.LV mechanical efficiency may tend to correlate linearly with the ventriculo-arterial coupling index, although the abnormal coupling between the left ventricle and arterial system still exists.