The effect of 20 amino acids and the synthetic tetrapeptide cardiogen in concentration 10(-12) M was investigated in organotypic tissue culture on the cell proliferation and apoptosis development in myocard tissue explant in 3- and 24-months old rats. 7 of 20 amino acids stimulated the cell proliferation in the young rats. In the same time, only 2 amino acids were active in myocard culture from the old rats. The tetrapeptide cardiogen demonstrated the great stimulating effect on the proliferation both in tissues from young and old rats. The immunohistochemical study demonstrated a decrease of the p53 protein expression by cardiogen action. This fact can testify that cardiogen inhibits the apoptosis process in the myocard tissue.