Extended pluripotent stem cells (EPSCs) possess a high differentiation capacity, potentially as a superior seed resource for generating cardiomyocytes. Here, we present a protocol for generating feeder-free EPSCs (ffEPSCs), cardiomyocytes, and engineered heart tissues (EHTs). We describe steps for converting human embryonic stem cells or induced pluripotent stem cells (ESCs/iPSCs) into ffEPSCs, followed by their long-term maintenance, cryopreservation, seed preservation, and differentiation into cardiomyocytes. We then detail procedures for constructing and culturing three-dimensional EHTs followed by their contraction force measurement and optical mapping. For complete details on the use and execution of the protocol, please refer to Zheng et al.