When the heart is faced with an increased work load on a chronic basis, cardiac hypertrophy results. With aging, certain changes occur in the cardiac cell which may alter the response to a chronically imposed work load, i.e., there may be an interaction of the adaptation to this stress and aging. The present studies were undertaken to determine whether such an interaction could be demonstrated. The elucidation and understanding of such an interaction is central to the well known observation that cardiac pathologic conditions that impose an increased work load become more severe with aging or the passage of time.