Stem cell therapy holds great promise for the treatment of injured myocardium, but is challenged by a limited supply of appropriate cells. Three different isoforms of transforming growth factor-beta (TGF-beta) -beta 1, -beta 2, and -beta 3 exhibit distinct regulatory effects on cell growth, differentiation, and migration during embryonic development. We compared the effects of these three different isoforms on cardiomyocyte differentiation front embryonic stem (ES) cells. In contrast to TGF-beta 1, or -beta 3, treatment of mouse ES cells with TGF-beta 2 isoform significantly increased embryoid body (EB) proliferation as well as the extent of the EB outgrowth that beat rhythmically. At 17 days, 49 % of the EBs treated with TGF-beta 2 exhibited spontaneous beating compared with 15 % in controls. Cardiac myocyte specific protein markers sarcomeric myosin and alpha-actin were demonstrated in beating EBs and cells isolated from EBs. In conclusion, TGF-beta 2 but not TGF-beta 1, or -beta 3 promotes cardiac myocyte differentiation from ES cells. (c) 2005 Elsevier Inc. All rights reserved.