The effects of aminophylline on pulmonary vascular tone, systemic hemodynamics, and ventricular ejection fractions reported in the literature show some discrepancies. We therefore studied in COPD patients the effects of aminophylline on hemodynamics, on ventricular ejection fractions, and on systolic and diastolic functions of each ventricle, and we measured simultaneously the blood level of the drug. The analysis of the data revealed a relationship between the blood level of aminophylline and the variations of right ventricular ejection fraction (RVEF) (r = 0.83, p = 0.005), left ventricular ejection fraction (LVEF) (r = 0.76, p = 0.017), pulmonary vascular resistance index (PVRI) (r = -0.58, p = 0.096), systemic vascular resistance index (SVRI) (r = -0.60, p = 0.08), and right ventricular peak systolic pressure/end-systolic volume index (RVPSP/ESVI) (r = -0.75, p = 0.02). Modifications of ejection fractions and vascular resistance indices were correlated for both ventricles (RVEF vs PVRI, r = -0.77, p = 0.01; LVEF vs SVRI, r = -0.76, p = 0.02). Finally, RVEF modifications was also correlated to RVPSP/ESVI variation (r = 0.78, p = 0.01). These results suggest that even within the therapeutic range (10 to 20 mg/L), the effects of aminophylline seemed to depend on its blood level. This dose dependency could explain the contradictory data reported in the literature concerning the effects of aminophylline on pulmonary and systemic hemodynamics and on ventricular function.