Beta blockers may benefit patients with dilated cardiomyopathy but low output failure can be a problem. Thus a beta 1-selective beta blocker with about 45% intrinsic sympathomimetic activity (ISA), such as xamoterol, was thought to have a desirable pharmacologic profile. Long-term studies of xamoterol in patients with idiopathic dilated cardiomyopathy have shown improved cardiac performance and exercise tolerance, while exercise heart rate, left ventricular ejection fraction, and pulmonary artery wedge pressure were decreased. This improvement in exercise capacity and overall quality of life in patients treated with xamoterol has been confirmed in further controlled trials of patients with mild-to-moderate heart failure (NYHA class I and II). However, in patients with moderate-to-severe heart failure (NYHA class III and IV), mortality was unfavorably influenced by xamoterol. The therapeutic role of xamoterol in patients with heart disease needs further refinement.