Heart is the first functional organ in a developing embryo. One critical step during vertebrate heart development is trabeculation, which is crucial for heart function. During trabeculation, the myocardial wall transforms from a single-layered epithelium into a complex topological structure consisting of two distinct cell fates – outer compact layer and inner trabecular layer cardiomyocytes. We have recently shown that local differences in the mechanical properties of CMs trigger this morphological symmetry breaking. CMs with higher mechanical tension delaminate stochastically to seed the trabecular layer and this spatial segregation is also sufficient to induce their differential fate. Eventually, these single trabecular cells undergo complex morphological transformations to generate higher-order multicellular structures called trabecular ridges, which fill the ventricular lumen. How a developing heart acquires these crucial anatomical structures remains unknown. My lab aims to resolve the underlying mechanical, molecular and geometric interactions that transforms the myocardial wall from a simple epithelium into a 3D intricate functional tissue. In this seminar, I will be discussing some of our previous and current findings explaining how trabecular cardiomyocytes are specified and how a single trabecular cardiomyocyte build the multicellular ridge.