During normal cardiac development of vertebrates, the embryonic heart starts as a straight tube along the midline of the embryo. It subsequently transforms into a c-shaped heart loop reliably toward the right side of the body. This cardiac c-looping is the earliest evident event of left-right asymmetry breaking (also called chirality or handedness) of a human organ. The inversed lateralization (i.e., toward the left side) of cardiac looping often leads to severe clinical outcomes, including dextrocardia, septum defects, double outlet right ventricle, and even death of fetuses and infants. In the past, we have been able to recapitulate multicellular chiral morphogenesis in vitro and shown that cardiac cells from chick hearts right before looping have an intrinsic rightward bias. Also, protein kinase C activators, newly identified regulators of cardiac cell chirality, can reverse chick cardiac c-looping. In the funded R01 grant (HL148104), we proposed to investigate how intrinsic cell chirality determines asymmetric cardiac looping biochemically and biomechanically. We now request a research supplement to address a Reviewers’ concern (relevance to human diseases) by using human cardiac cells and investigating the role of the planar cell polarity (PCP; also called noncanonical wnt) signaling, a pathway known for cardiac laterality defects. We hypothesize that PCP regulates the scale of multicellular chiral morphogenesis and cardiac c-looping. To test the hypothesis, we propose to evaluate the expression of PCP proteins and assess the role of PCP proteins in forming 2D in vitro multicellular chiral patterns and ex ovo looping hearts in chick embryonic development. Specifically, we will first assess the polarity and chirality of PCP markers in patterned human cardiac cells. We will pattern cardiomyocytes in 2D, examine the location and morphology of the PCP markers, and determine how PCP signals biomechanically regulate chiral morphogenesis. Then, we will determine the role of PCP signaling in chick cardiac c looping. With the chick ex ovo culture, we will evaluate the localization of PCP proteins during the looping stages, interfere with PCP signaling to examine the effects of PCP, and use cell vertex-based numerical simulation to assess the biomechanical role of PCP signaling in the asymmetric heart looping. Overall, the proposed research will delineate the role of PCP signaling in chiral multicellular morphogenesis and in early cardiac asymmetric looping.