Background Carvedilol may reduce the severity of central sleep apnea (CSA) in patients with chronic heart failure (CHF). Methods and Results This study prospectively examined the effect of carvedilol on the severity of CSA in patients with CHF. Polysomnographic findings, left ventricular (LV) function, and plasma brain natriuretic peptide (BNP) level were evaluated before and 6 months after induction of carvedilol in 16 patients with CHF (New York Heart Association functional class II or III and LV ejection fraction <50%) who had CSA (central apnea index [CAI] >5 with dominant central apneic events). All patients tolerated carvedilol. The 6-month treatment with carvedilol increased the LV ejection fraction (32±7.4% to 45±9.8%, P<0.001) and decreased the BNP level (159 [69-458] pg/ml to 38 [16-193] pg/ml, P=0.017). The polysomnographic findings showed that the treatment decreased the apnea-hypopnea index (34±13 to 14±13, P=0.003) and CAI (13±11 to 1.9±4.3, P<0.001), whereas it increased the obstructive apnea index (1.1±1.5 to 3.1±3.4, P=0.04). Conclusion This preliminary study shows that treatment with carvedilol reduces the severity of CSA in patients with CHF, but that episodes of obstructive sleep apnea sometimes increase after the treatment. (Circ J 2009; 73: 295 - 298)