['Recent studies have demonstrated that cardiac resynchronization therapy (CRT) reduces sleep apnea in heart failure (HF); however, the mechanism of benefit remains unclear.', 'Overnight polysomnography (PSG) was performed in consecutive HF patients who were scheduled for CRT implant. Patients with sleep apnea defined by an apnea-hypopnea index (AHI) of >10/hour were recruited and underwent echocardiogram examination at baseline and 3 months after CRT.', 'Among 37 HF patients screened, 20 patients (54%) had sleep apnea and 15 of them consented for the study. After 3 months of CRT, there was a significant improvement in New York Heart Association functional class (3.1+/-0.1 vs 2.1+/-0.1, P<0.01), quality-of-life (QoL) score (62.9+/-3.3 vs 56.1+/-4.5, P=0.02), left ventricular ejection fraction (LVEF, 28.8+/-2.5% vs 38.1+/-2.3%, P<0.01), and reduction in pulmonary artery systolic pressure (PASP, 41.0+/-2.7 vs 28.6+/-2.2 mmHg; P<0.01) compared with baseline. Repeated PSG after CRT demonstrated a reduction in the duration of arterial oxygen desaturation<or=95% (251.2+/-36.7 vs 141.0+/-37.1 minutes), AHI (27.5+/-4.7 vs 18.1+/-3.0, P=0.05), and number of central sleep apnea (CSA) (7.8+/-2.6 vs 3.0+/-1.3/hour, P=0.03), but not number of obstructive sleep apnea (OSA, 8.6+/-3.3 vs 7.2+/-2.3/hour, P=0.65) compared to baseline. Percentage change in PASP was significantly correlated with percentage changes in LVEF (r=-0.57, P=0.04), AHI (r=0.5, P=0.05), and number of CSA episodes (r=0.55, P=0.02).'] Is alleviation of pulmonary hypertension by cardiac resynchronization therapy associated with improvement in central sleep apnea?