OBJECTIVE To explore the essential features of the potential distribution of electrocardiac field. METHODS The ECGs of 60 hearts of 5-day chick embryos were immersed in normal saline solution or distilled water and their different conductivities were recorded at 5 points at different distances in 4 directions perpendicular to each other. Comparison of the form and amplitude of ECGs was made between every two points with the same distance to the heart in 2 opposite directions to determine the potential distribution of the electrocardiac field of the one-chambered heart. RESULTS The ECGs recorded at every 2 points in 2 opposite directions with the same distance to the heart immersed in the same liquid medium were both upper standing, with no significant different between their amplitude of R(r) wave (P > 0.05). CONCLUSION The uniform outward potential distribution of the electrocardiac field might not represent the form of depolarization but that of sphere-like and single-source when the influence of different reference points and thickness of different chamber walls upon mapping of body surface is excluded.