L-3-hydroxyacyl-CoA dehydrogenase (HADH/HCDH) is a mitochondrial matrix protein expressed in pancreas, liver, heart, kidney and skeletal muscle. L-3-hydroxyacyl-CoA dehydrogenase catalyzes the oxidation of straight-chain 3-hydroxyacyl-CoAs as part of the beta-oxidation pathway. Its enzymatic activity is highest with medium-chain-length fatty acids. Mutations in this gene can lead to HADH (3-α-hydroxyacyl-CoA dehydrogenase) deficiency and familial hyperinsulinemic hypoglycemia 4 (HHF4).