Biventricular (BV) pacing acutely improves the hemodynamic status of patients with chronic heart failure (CHF) and wide QRS complex. Long-term data are few. This study examined the relationship between hemodynamic and clinical status of BV-paced CHF patients over an intermediate duration of follow-up. Forty-seven patients (mean age 64 +/- 11 years, 19% women, LVEF 0.23 +/- 0.07) with QRS > or = 140 ms received a DDD-BVP device for management of CHF due to ischemic disease in 21 (45%) patients. Clinical, electrocardiographic, exercise testing, and hemodynamic measurements were followed over an 8-month period. Seven patients died during the study, four patients suddenly. A significant decrease in NYHA class, from 3.3 +/- 0.6 before implantation, to 2.5 +/- 0.57 months after device implantation (P < 0.01) was measured, although 23% of patients reported no symptomatic improvement. Paced QRS narrowing by BVP was unchanged throughout follow-up (166 +/- 28 vs 159 +/- 23 ms, P = NS). Maximal VO2 values did not change (15.7 +/- 5 vs 16 +/- 8 mL/kg per min, P = NS). Echocardiographic parameters showed that the degree of mitral regurgitation was significantly decreased during BV pacing compared with no pacing (1.8 +/- 1.0 before implantation vs 1.3 +/- 0.7, P < 0.01). The radionuclide LVEF was not statistically different during no pacing, versus BV pacing at 3 months or 8 months after pacemaker implantation (24 +/- 9 vs 26 +/- 11 vs 25 +/- 10%, respectively, P = NS). Of nine patients whose QRS duration was prolonged by BV pacing, two were not hemodynamically and clinically improved at the end of follow-up. Patients not improved by BV pacing had the same degree of QRS shortening (203 +/- 39 vs 167 +/- 26 ms, P < 0.01) as patients who were clinically improved during follow-up (193 +/- 40 to 171 +/- 24 ms, P < 0.01). In multivariate analysis, ischemic heart disease (P = 0.025), absence of mitral regurgitation regression (P = 0.01), and older age (P = 0.04) predicted the absence of improvement by BV pacing. By standard noninvasive measures, intermediate-term BV pacing was associated with no objective hemodynamic improvement, though more than three fourths of the patients reported being clinically improved. A global improvement in left ventricular function by BV pacing may become apparent only over longer periods of observations. Patients with CHF unimproved by BV pacing are more likely to suffer from ischemic heart disease and less likely to have BV pacing induced regression of mitral regurgitation, regardless of changes in QRS duration.