Previous studies demonstrated that circulating regulatory T (Treg) cell levels decreased in patients with stable heart failure. However, whether and how the levels of Treg cells change in patients with acute decompensated heart failure (ADHF) has not yet been investigated. The present study was designed to investigate the dynamic changes in CD4(+)CD25(+) Treg cell activity that occur in ADHF patients. Forty patients with ADHF, 20 patients with chronic stable heart failure (CSHF) and 20 healthy subjects were enrolled in the present study. The frequencies of CD4(+)CD25(+) Treg cells were detected using flow cytometry analysis, and plasma IL-10 and TGF-beta 1 levels were measured using ELISA. The results revealed a significant decrease in CD4(+)CD25(+) Treg cell frequencies and IL-10 and TGF-beta 1 levels in ADHF patients at admission in comparison with the CSHF and control groups. The CD4(+)CD25(+) Treg cell frequencies and IL-10 and TGF-beta 1 levels were higher in the ADHF patients at discharge than at admission. No differences were observed between the ADHF patients at discharge and the CSHF patients. In addition, the CD4(+)CD25(+)FOXP3(+) T cell frequencies and IL-10 and TGF-beta 1 levels were significantly decreased in class III patients relative to class II patients at discharge. Our findings indicate that ADHF is associated with low CD4(+)CD25(+) Treg cell activity at admission. Although these abnormal levels are improved after treatment, the values remained lower in ADHF patients at discharge than in healthy subjects.