AbstractBackground: Enhanced external counterpulsation (EECP) has been demonstrated to be an effective treatment for angina and exertional ischemia in patients with coronary disease.Hypothesis: It is hypothesized that the ability of EECP to enhance the recruitment or development of coronary collaterals in coronary artery disease may be determined by the relative magnitude of diastolic augmentation (DA) and systolic unloading (SU). This study examines the relation between the proposed EECP effectiveness ratio (DA/SU), as assessed by finger plethysmography, and changes in descending aortic flow as assessed by Doppler echocardiography in 15 patients during EECP.Methods: Varying external cuff pressures (0‐275 mmHg) were used to generate a range of DA/SU ratios. The effect on aortic antegrade systolic and retrograde diastolic flow was assessed by Doppler echocardiography to determine whether there was an optimal EECP effectiveness ratio that maximizes the hemodynamic effects of EECP. With increasing DA/SU there was an initial positive linear increase in both systolic and diastolic flow volume. Systolic flow maximized at an effectiveness ratio of 1.5 and diastolic flow at a ratio of 2.0.Result: Therefore, effectiveness ratios (DA/SU) in the range of 1.5‐2.0 are optimal for maximizing the hemodynamic effects of EECP.