Cardiac tissue engineering has major applications in regenerative medicine, disease modeling and biological studies. Despite the significance, numerous questions still need to be explored to enhance the functionalities of engineered tissue substitutes. In this study, 3D cardiac microtissues are developed through encapsulation of cardiomyocytes and cardiac fibroblasts, as the main cellular constituents of native myocardium. The geometries of the constructs are precisely controlled and assessed for their role on synchronous contraction of the cells. Cardiomyocytes exhibit a native-like phenotype when co-cultured with cardiac fibroblasts as compared to the monoculture condition. Particularly, elongated F-actin fibers with abundance of sarcomeric α-actinin and troponin-I are observed within all layers of the constructs. Higher expressions of connexin-43 and integrin-β1 indicate improved cell-cell and cell-matrix interactions. Amongst co-culture conditions, 2:1 (cardiomyocytes: cardiac fibroblasts) ratio exhibits enhanced functionalities, whereas decreasing the construct size adversely affects the synchronous contraction of the cells. Overall, the study here indicates that the cell-cell ratio and the construct geometry are crucial parameters, which need to be optimized to enhance the functionalities of the engineered tissue substitutes.