ACE2 and heart failure: However, the relationship of tissue ACE2 expression and circulating ACE2 activity is still not well understood and data from the literature is partial contradictory (23): in human, the ACE2 activity was shown to be higher in healthy men and men with heart failure compared to matched women (28, 29) while other studies showed no sex-related differences in serum ACE2 activity (30, 31).