Monitoring the electrophysiology of living cells by micro/nano devices is a well-established technique in a large area of biomedical applications. The main fascination is the ability of these devices to perform, in real-time, non-invasive investigations of the physiological state of a cell population. In this work, we present a hybrid microsystem model to detect extracellular signals induced by cardiac cells (CDs). In particular, the bio-electronic junction established by interfacing cardiac cells to Carbon NanoTubes (CNTs) vertically grown on the surface of a metal microelectrode (MIC) was modeled to analyze the induced extracellular cell electrical activity. The simulation results strengthened the assumptions that CNTs, as electrical interfaces, enhance the amplitude and act on the shape of the recorded extracellular signals, compared to other microelectrode substrates.