Continuous positive airway pressure (CPAP) causes a variable immediate reduction in the frequency of central apnoeas and hypopnoeas in patients with congestive heart failure (CHF) and central sleep apnoea (CSA), but has beneficial mid-term effects on factors known to destabilize the ventilatory control system. We, therefore, tested whether CPAP therapy leads, in addition to its short-term effects on CSA, to a significant further alleviation of CSA after 12 weeks of treatment on the same CPAP level in such patients. CPAP therapy was initiated in 10 CHF patients with CSA. During the first night on CPAP, the pressure was stepwise increased to a target pressure of 8-12 cmH(2)O or the highest level the patients tolerated (<12 cmH(2)O). Throughout the second night (baseline CPAP), the achieved CPAP of the first night was applied. After 12 weeks of CPAP treatment, we performed a follow-up polysomnography (12 weeks CPAP) on the same CPAP level (8.6 +/- 1.1 cmH(2)0). We found a significant reduction of the apnoea-hypopnoea index (AHI) between the diagnostic polysomnography and baseline CPAP night (41.8 +/- 19.2 versus 22.2 +/- 12.6 events per hour; P = 0.005). The AHI further significantly decreased between the baseline CPAP night and the 12 weeks CPAP night on the same CPAP level (22.2 +/- 12.6 versus 12.8 +/- 11.0 events per hour; P = 0.028). We conclude that, in addition to its immediate effects, CPAP therapy leads to a time-dependent alleviation of CSA in some CHF patients, indicating that in such patients neither clinical nor scientific decisions should be based on a short-term trial of CPAP.