FNDC5 and congestive heart failure: The authors correlated these findings with total antioxidant capacity (TAC), as an index of oxidative stress, and found an inverse correlation between irisin and TAC in HFpEF but not in HFrEF, which led them to conclude that different pathophysiological mechanisms are involved in the two CHF subtypes, and that oxidative stress modulates irisin secretion [8].