Cardiac Resynchronization Therapy, Dyspnea and Exercise Tolerance in Patients With Congestive Heart Failure (CHF)

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