Two small studies have assessed the hemodynamic response to dobutamine in the presence and absence of beta blocker therapy in patients with chronic heart failure. In addition, one of these studies assessed the response to enoximone, another phosphodiesterase III inhibitor. Both studies demonstrated that metoprolol did not significantly affect the hemodynamic response to dobutamine infusion, including its effect on cardiac index, heart rate, stroke volume, and systemic vascular resistance. Conversely, carvedilol was shown to have significant inhibitory effects on cardiac index, heart rate, and stroke volume during dobutamine infusion. In addition, carvedilol appeared to increase mean arterial pressure at higher doses of dobutamine. In the setting of an enoximone infusion, metoprolol increased the cardiac index and stroke volume responses, while maintaining other hemodynamic parameters. There was no significant difference in the hemodynamic response to enoximone infusion in the presence of carvedilol.