V ascular endothelial growth factor (VEGF) is an endothelial cell mitogen involved in vascular development and angiogenesis. Recently we have observed increased VEGF expression in the normal myocardium after myocardial infarction in a rat heart. This study was designed to explore the mechanism responsible for this increase in VEGF expression. Induction of myocardial stretch in an isolated perfused Langendorff preparation by inflation of an intraventricular balloon to an end-diastolic load of 35 mmHg for 30 min resulted in a nearly sixfold increase in VEGF message level not only in the chamber subjected to stretch (left ventricle) but also in the unstretched right ventricle, thus raising the possibility of a soluble factor mediating stretch- induced induction of VEGF expression. This was further confirmed by demonstrating that coronary venous effluent collected from the stretched heart and used to perfuse isolated hearts in which no balloon was present was able to induce VEGF expression in these normal hearts. Inhibition of TGF-beta activity using a neutralizing antibody, but not antagonists/inhibitors of endothelin and angiotensin II, eliminated stretch-induced increase in VEGF expression. Staurosporine, a protein kinase C inhibitor, also blocked stretch-induced increase of VEGF expression. Measurement of TGF-beta concentration in the perfusate demonstrated increased amounts of the cytokine after myocardial stretch, and addition of TGF-beta protein to the perfusion buffer resulted in increased VEGF expression in control hearts. These results suggest that stretch-induced increase of VEGF expression in the heart is mediated at least in part by TGF-beta.