The morphogenetic Planar cell polarity (PCP) pathway is known to govern cellular behaviors within tissues and organs by coordinating polarized cell adhesion and actomyosin activity. Yet, the possible effects of PCP signaling on the nuclear compartment have not been explored. Here, we discovered PCP signaling directs nuclear mechanics of the heart muscle cells in the developing heart. The cardiomyocyte nuclei undergo profound morphological changes specifically during embryonic remodeling of early heart tube to chambered heart, in both fish and mice. The changes in cardiomyocyte nuclear morphology require contractile actomyosin through the function of Vangl2, a key PCP component. Moreover, Vangl2 regulates nucleocytoplasmic actin homeostasis by altering the ratio of globular actin within the nucleus. We discovered the Vangl2-dependent nuclear morphology is linked to transcriptional changes in gene programs regulating muscle differentiation. Functionally, the nuclear dynamics occurring specifically in the early linear heart tube are required for proper sarcomerogenesis and muscle differentiation in the late cardiogenesis. Thus, PCP signaling known for sculpting tissues through its effects on actomyosin, utilizes the same machinery to regulate the gene expression of the organs it shapes.