During early embryogenesis, the heart is a single, relatively straight tube which bends and twists (loops) rightward to create the basic plan of the mature heart. Despite intensive study for many decades, the biophysical mechanisms which drive and regulate cardiac looping have remained poorly understood. This review discusses, from a historical perspective, studies of looping mechanics and various theories which have been proposed for this complex process. Then, based on recently acquired data, a new biomechanical hypothesis is proposed for the rst phase of looping (c-looping). Understanding morphogenetic mechanisms would facilitate research devoted to preventing and treating congenital heart malformations caused by looping abnormalities.