NAMPT and hyperinsulinemic hypoglycemia, familial, 4: NAD+ deficiency in failing heart tissues has been mainly attributed to decreased NAD+ salvage synthesis secondary, for example, to decreased expression of nicotinamide phosphoribosyltransferase (NAMPT), a rate-limiting enzyme in the NAD+ salvage pathway that catalyzes the conversion of nicotinamide (NAM) to nicotinamide mononucleotide (NMN) (Diguet et al, 2018; Matasic et al, 2018), which is subsequently converted to NAD+ by nicotinamide mononucleotide adenylyl transferases (NMNATs) (Tatsumi et al, 2019).