To investigate the plasma drug level, efficacy, and safety of 7-day repeated oral administration of OPC-41061 at 15 mg/day (treatment period 1) and subsequent 7-day repeated administration of OPC-41061 at 15 mg/day or 30 mg/day if diuretic effect is insufficient (treatment period 2) in congestive heart failure (CHF) patients with extracellular volume expansion despite conventional diuretic therapy.