Cardiac c-looping is an important developmental phase, as the initially straight heart tube (HT) is transformed into a c-shaped tube. Looping consists of two distinct processes: ventral bending, which is likely driven by actin polymerization, and dextral torsion, which is likely due to external forces. These forces are applied by a membrane enveloping the ventral side of the heart, the splanchnopleure (SPL, Fig. 2A) and a pair of atria that flank the caudal end of the heart tube (HT, Fig 1A). In particular, the atria provide the initial push, biasing the HT towards the right while the SPL applies a ventrally directed force, which causes the HT to rotate using the dorsal mesocardium (DM, Fig. 2A) as a pivot (the DM attaches the dorsal length of the heart to the body of the embryo).

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