Hemodynamic overload induces cardiac hypertrophy (CH). The signals which initiate and maintain the hypertrophic response have not been elucidated. The aim of the present study is to identify growth stimulators which are produced by the post-natal heart, the expression of which are increased by hemodynamic overload. for this purpose rats are exposed to hemodynamic overload, and hearts are excised at different stages after the intervention, weighed, and the level of growth factors, their receptors and RNA encoding them are checked. RNA encoding for several major growth factors and their receptors was detected by means of northern blots and RNAse protection assays. These include: insulin like GF - I and II and their receptors, transforming GF-beta, and platelet derived GF. We are now determining if these messages differ between normal and hypertrophied or hypertrophying hearts.