Serum ACE2 activity levels were determined in healthy people (healthy, n = 45, filled bar, panel A), patients with no apparent heart failure (hypertensive, n = 239, grey bar, panel A) and in patients with severe systolic heart failure (HF - CRT before, n = 100, open bars, panel A). Patients were also evaluated with respect of their New York Heart Association (NYHA) functional class (HF - CRT before: NYHAII: n = 31; NYHAIII: n = 55; NYHAIV: n = 14, panel B; HF - CRT after: NYHAI: n = 17; NYHAII: n = 37; NYHAIV: n = 11, panel C). Serum ACE concentration was also determined with respect of the New York Heart Association (NYHA) functional class of the patients before (HF – CRT before, panel D) and after CRT (HF – CRT after, panel E). Statistical analyses of healthy people, hypertensive, HF - CRT before and HF – CRT after groups were performed by one-way analysis of variance (ANOVA) followed by Newman-Keuls test for multiple comparisons between groups. Bars are mean ± S.E.M. Significant differences are labeled by asterisks (** P<0.001).