In 1956, Bruno Kisch (90) discovered a special form of myocyte in the guinea pig heart atrium which contained peculiar, dense inclusions, but it was not before the early 1980s that cardiac hormones were isolated and characterized independently and almost simultaneously by several working groups. In 1964 Jamieson and Palade (84) were the first to postulate the secretory nature of the atrial myocytes and their specific granules. In 1976, Marie et al. (103) revealed the relation of the granular index of these atrial cells with the water- electrolyte balance of the body fluid. The biological...