The dextral heart looping is the first morphological manifestation of left-right (L-R) asymmetry during vertebrate development. There is a well-established genetic pathway underlying the rightward heart looping process in the chick. Pitx2, a bicoid-related homeobox gene, plays a critical role in L-R determination and resides downstream of the Shh/Nodal signaling pathway Three isoforms of Pitx2 have been identified in mouse and human. Only two Pitx2 isoforms, Pitx2a and Pitx2c, were isolated from the chick embryo. These two isoforms only differ in the region 5' to the homeodomain. RT-PCR and northern blot analyses verified the existence of Pitx2a and Pitx2c but not Pitx2b in the developing chick embryo. Pitx2c but not Pitx2a is expressed in the left lateral plate mesoderm (LPM). Both isoforms equally encode a transcription activator. Ectopic expression of Pitx2c and Pitx2a to right LPM randomize heart looping. Loss-of-function studies indicate that Pitx2c play a predominant role in the regulation of heart looping in the developing chick embryo Using of gain-of-function and loss-of-function approaches, the extracellular matrix molecule flectin is confirmed to be the downstream effector of Pitx2c. It has been shown that BMP is involved in specification of L-R development. In this study, the role of the BMP receptors in the heart looping was investigated. I found that only BMPIA but not BMPIB was capable of randomizing heart looping when overexpressed on the left LPM. It was also demonstrated that BMPIA might mediate a Pitx2 independent pathway that also regulates heart looping in the chick