The spontaneously hypertensive rat (SHR) is a well studied animal model of genetic hypertension and heart disease of unknown cause. With the use of differential display, a transcript was found in SHR myocardium that on sequence analysis was identified as an endogenous retrovirus (ERV). ERV gene expression was greater than an order of magnitude increased in adult SHR hearts relative to age-matched normotensive Wistar-Kyoto rats and was further increased in hearts from SHR with heart failure. In situ hybridization studies demonstrated that increased ERV gene expression was localized to myocardial cells. Increases in ERV transcripts in SHR suggest a possible link between inherited proviral elements and genetic hypertensive heart disease. (Hypertension. 1997;30[part 1]:88-93.)