Beta-blocker medications have been shown to improve heart function and prolong the lives of patients with chronic heart failure (CHF). Some people with advanced CHF have difficulty taking beta-blocker medications due to troublesome side effects, such as low blood pressure and/or low heart rate, severe tiredness, dizziness, or shortness of breath. In other words, they have difficulty tolerating beta-blocker medications. The purpose of this study is to determine if enoximone can improve a patient's ability to tolerate a beta-blocker medication.