The objective of this study was to determine the effect of body characteristics on the electrical transfer function of the human thorax. Twenty patients undergoing electrophysiologic study were enrolled. Unipolar stimuli were applied in the right ventricular apical and posterioseptal areas. XYZ surface ECGs and unipolar intra-cardiac electrograms of the pacing impulses were recorded and signal-averaged. The intracardiac-to-surface transfer functions were modeled and compared with body characteristics. Physical dimensions, respiratory measures obtained by spirometry, and age correlated with magnitude intercepts and slopes of the modeled transfer functions in all three directions. The phase transfer functions were correlated with physical dimensions in the Y and Z directions. The effect of body characteristics on the frequency dependency of attenuation and phase has implications on the use of surface ECG and body surface mapping.