Summary The neural cell adhesion molecule, NCAM, is present in several non-neuronal tissues including heart. Using biochemical methods it has been recently shown that NCAM is expressed on cardiac myocytes in early development. During postnatal development NCAM expression is down-regulated and is restricted to neural components of rat heart. However, in the aged rat heart NCAM expression is increased compared to young adult rats. In the present immunohistochemical study the localization of NCAM in different regions of aging rat heart was investigated. Cardiac myocytes expressed NCAM in newborn rat heart whereas NCAM was absent from myocytes in young adult heart. In aged rat heart, NCAM was reexpressed on cardiac myocytes in the ventricles. Thus, NCAM reexpression may be an element in regenerative processes or alternatively a marker of degenerating or dying myocytes