Although breeders, owners and veterinarians who work with Norfolk Terriers are suspicious that an early onset form of mitral valve disease exists in this breed there have been no published studies to characterize mitral valve disease in the Norfolk. The goal of the proposed study is to investigate the incidence, pattern of inheritance, progression, pathology and potentially the genetic basis of mitral valve disease in the Norfolk Terrier. This information will benefit the breeder, veterinarian and pet owner by providing the information necessary to make informed medical and breeding decisions. In addition, this study proposes the development of a canine cardiac gene array. This array has the potential to increase our understanding about a variety of cardiac disorders by providing a screening tool for expression of a subset of cardiac genes.