Engineering heart-like organoids in vitro holds significant promise for advancing cardiovascular research. While current approaches, such as suspended cell clusters in media or encapsulating them in gels, have shown potential, they are often challenged in generating organoids with defined chambers and synchronized contractions due to variations in outcomes linked to cell density. In this study, we present a strategy to modulate cell-cell interactions at a fixed cell density by mimicking bioprocesses underlying embryo implantation and invasion. Specifically, an embryoid body cultured on a collagen-poly(ethylene glycol) gel with greater porosity and hydrophilicity and lower stiffness than a pure collagen gel undergoes enhanced invasion and self-organization, resulting in functional, embryo-like cardiac organoids. These organoids exhibit distinct chamber structures surrounded by cardiac muscle, pacemaker cell innervation, atrioventricular synchrony-like contractions, recurring calcium flux, and electrocardiogram-like signals. Organoid development is associated with upregulated expression of mesodermal, ectodermal, and N-cadherin genes. This simple yet effective approach will enable robust modeling of heart physiology and drug response in vitro, offering valuable insights for translational cardiovascular research.