Atrial and ventricular fibrillations are thought to be caused by multiple chaotically wandering wavelets of excitation of unknown origin. We aimed thus to provide new insights into the cellular origin of the fibrillation phenomenon by exploring the impulse propagation between cardiac myocytes in confluent monolayers of cultured cardiomyocytes (CM), which beat spontaneously and synchronously. Multisite field potentials have been recorded using microelectrode arrays (MEA) technology in basal conditions and in proarrhythmic conditions. CM were grown on multi-electrode arrays (MEA) allowing non-invasive synchronous multifocal field potential (FP) recordings. The MEA consists of 60 substrate-integrated microelectrode arrays (8×8 matrix, 30μm electrode diameter, 200μm inter-electrode distance). Data were real time acquired and analyzed with a customized platform programmed with MATLAB (Mathworks) in order to provide two-dimensional electrophysiological maps derived from these multisite FP recordings, in particular the contour of the FP propagation wavefront during each period. The sets of activation maps were then used to reconstruct videos revealing multicycle spatiotemporal patterns. In basal condition, the observation of these activation maps indicated that the spontaneous FP spikes propagated following linear path, with very stable periodic characteristics. Cardiomyocytes were then stimulated by an external electrical signal, consisting in a stimulation train (burst of 200mV at 100Hz during 5min) in one point at the edge of the MEA. After this stimulation protocol, the recorded electrical activities became irregular, as confirmed by Poincaré maps of the FP periods. Moreover, spiral waves (SW) appeared in the cardiac cell network. These SW were unstable in location and could move inside or outside the recording area. SW had a mean radius of 400×100μm and a mean angular velocity of 225×30 rotations per minute. Unstable reentrant and colliding wavefronts were also observed. To conclude, SW can be precisely characterized using a MEA data acquisition system. Therefore, within the limitations inherent to the preparation used, the cultured CM monolayer is a controlled experimental model that may be useful for further studies on the basic aspects of fibrillation and defibrillation.