Stopped due to an inability to recruit eligible subjects.

A new therapy for patients with advanced heart failure (HF) involves the implantation of a specialized pacemaker device (Cardiac Resynchronization Therapy, CRT) that attempts to restore the synchronized contraction of the ventricular chambers of the heart. In some people, CRT improves exertional breathlessness and allows them to exercise for longer periods. However, to date, the mechanisms by which CRT improves symptoms and exercise tolerance is unknown. This study will use in-depth cardiopulmonary exercise testing and pulmonary function testing to explore these mechanisms in greater detail.

Inclusion Criteria:

• clinically stable
• being considered for implantation of biventricular pacemaker for CRT
• LVEF <35%
• QRS duration >120 msec
• NYHA III-IV functional class
• optimized pharmacologic management of CHF
• no recent (<1 month) episodes of decompensated CHF

Exclusion Criteria:

• inability to perform cycle ergometry or comply with testing
• uncontrolled ischemic heart disease
• coronary revascularization within 3 months of study entry
• concurrent primary lung disease
• current use of ambulatory oxygen
• rhythm other than sinus
• dependency on pacemaker therapy as a consequence of bradyarrhythmias
• severe valvulopathy