This research will test the hypothesis that all of the diagnostic information obtainable from a catheter-electrode recording from the heart's endocardial surface, near the bundle of His and the bundle branches, is also available by appropriate recording from the body surface. We will attempt to overcome the problem of signal-to-noise ratio and choice of surface electrode sites by a number of techniques. After visual and temporal verification that activity is likely arising from the His-Purkinje system, we will apply already existing computer programs and transfer matrices to examine the three dipolar or vectorial leads and an additional 20 scalar leads of the multipolar series. Leads particularly sensitive to signals temporally assignable to His-Purkinje activity will be searched for. Parallel animal work will occur. Finally, we expect a computational model of the sinoventricular conduction system to give insight into the interpretation of the observed data, to provide clues as to which surface lead arrays should prove most fruitful in both the direct recording and the multipolar analysis, and to suggest the possible direct contribution of the Purkinje activation to the early QRS complex.