The percentage of CD4(+) T cells in blood is correlated with left ventricular dysfunction and decreased ejection fraction in heart disease. The aim of this study was to determine the relation between activation of CD4(+) T cells and New York Heart Association functional classes in chronic heart failure (HF) and differences in inflammatory activation between ischemic cardiomyopathy (IC) and idiopathic dilated cardiomyopathy (IDC). Blood samples were obtained from 47 patients with HF and 20 controls. Percentages of interferon-gamma-positive CD4(+) T cells (representative type 1 T-helper cells) and interleukin-4-positive CD4(+) T cells (representative type 2 T-helper cells) were analyzed using 3-color flow cytometry. The proportion of interferon-gamma-positive CD4(+) T cells was higher in patients with HF (28.96 +/- 12.90%) than in controls (18.12 +/- 5.28, p = 0.0006), but there was no difference in percentage of interleukin-4-positive CD4(+) T cells between the 2 groups. The proportion of interferon-gamma-positive CD4(+) T cells and plasma B-type natriuretic peptide levels increased with worsening of New York Heart Association functional class in the IC and IDC groups. The proportion of interferon-gamma-positive CD4(+) T cells in the IC group (33.88 +/- 13.33%) was higher than in the IDC group (22.33 +/- 8.88%, p = 0.002); however, plasma B-type natriuretic peptide levels were higher in the IDC group (358.0 pg/ml, 327.5 to 1,325.7) than in the IC group (82.7 pg/ml, 34.7 to 252.9, p = 0.019). In conclusion, we demonstrated pronounced type 1 T-helper cell activation in patients with HF in proportion to severity of HF and that the specificity of T-cell activation differs between patients with IC and those with IDC.