The bioavailability of H2S is reduced proportionally to the severity of heart failure: a study of 124 patients with varying degrees of congestion showed total sulfur concentrations of ≈5.3 [2.2–8.0] μM versus 8.5 [6.0–14.0] μM in healthy controls, and the decline was accompanied by reduced endogenous capacity to produce H2S and depressed CSE activity [91]. This evidence concerns the gene CTH and heart failure.