Cats cannot synthesize enough taurine internally and must obtain it from animal-based protein in their diet. Before commercial cat foods routinely added taurine, feline dilated cardiomyopathy (DCM) was common. Today, deficiency most often occurs in cats fed dog food, vegan diets, or improperly formulated homemade diets. Certain dog breeds, particularly large breeds, may also be susceptible to taurine-related DCM, and some grain-free diets have been investigated for a possible association. Early signs include lethargy, reduced appetite, and difficulty breathing. Diagnosis involves blood taurine levels and echocardiography. Caught early, supplementation can reverse cardiac changes. Prevention is straightforward: feed cats a complete-and-balanced diet with adequate animal protein.