Closed loop systems, in which stimulation parameters are adjusted according to recorded signals would reduce the occurrence of side effects of stimulation and broaden current therapeutic options. As a step towards a closed-loop clinical system, we developed a single electrode stimulation / recording system for an in vitro microelectrode array. The system was used in vitro to simultaneously stimulate and record cardiac cells. Results indicated that stimulation artifacts depend on the distance between recording electrode and stimulating electrode and on the voltage amplitude. No artifact reduction algorithm was required for detecting cardiac action potentials 2ms after stimulation if the stimulation pulses were less than or equal to ± 1.5 V, and the distance from stimulation site was more than 200 µm. Cardiac signal propagation was also investigated with this system.