Unlike most mammals, cats have a very limited ability to synthesize the beta-amino acid taurine endogenously from precursor amino acids like methionine and cysteine, due to low activity of the enzymes cysteine dioxygenase and cysteinesulfinic acid decarboxylase. Consequently, taurine is an essential dietary nutrient for felines. Taurine is found in high concentrations in the myocardium and retina, where it functions in osmoregulation, modulation of intracellular calcium flux, and antioxidant defense. A dietary deficiency leads directly to dilated cardiomyopathy (DCM), characterized by progressive myocardial failure and ventricular dilation, as well as feline central retinal degeneration (FCRD), which causes irreversible blindness. Modern commercial feline diets are strictly fortified with taurine to prevent these potentially fatal conditions.