Dilated cardiomyopathy (DCM) is the most common acquired cardiovascular disease of dogs. Of suggested nutritional causes, taurine deficiency appears most evinced. But in dogs, such a need for dietary taurine is not generally recognized. Dogs are known to have the metabolic capacity to synthesize taurine from the dietary sulfur amino acids, cysteine and methionine (Hayes 1988). Diet-related taurine deficiencies and associated dilated cardiomyopathies have been reported in large breed dogs (Torres et al. 2000). The present investigators (Backus et al. 2000) have recently reported taurine deficiency (52 percent) and cardiac insufficiency (10 percent) among a group of 21 privately owned Newfoundland dogs. The proposed research will estimate the prevalence of a possible unrecognized, widespread, taurine deficiency in the Newfoundland breed. This will involve conducting non-invasive tests in a clinical setting. Dogs will be evaluated for heart and retinal disease. In selected normal and taurine deficient dogs, blood and urine will be collected to determine taurine and sulfur amino acid concentrations. Feeding trials will evaluate the effect of diet composition on taurine concentrations and excretion. A possible genetic contribution to taurine deficiencies will be assessed by pedigree analyses.