Propagation velocities and differential voltages of the electromotive surface in the left ventricle were measured in dogs by multipoint bipolar intramyocardial electrodes. The average velocity of propagation in the inner 4 mm of the ventricular wall of dogs was 2.0 mm/msec, which is considerably greater than that in the middle (0.70 mm/msec) or the outer 4 mm (0.40 mm/msec). The average voltage was less in the inner levels of the ventricular wall than in the outer, but significantly different from zero. This fact indicates a definite but lesser contribution per unit volume than from the outer levels. The propagation of the electromotive surface through the ventricular wall was consistently from endocardium to epicardium with no significant areas propagated in the reverse direction.These data disagree with the hypothesis that certain levels in the wall of the heart and certain regions of the heart are electrocardiographically silent. In dogs, and to a greater degree in humans, small infarcts anywhere in the heart can be expected to produce significant and discernible changes in surface ECGs. The task remains to refine and validate criteria for the diagnosis of infarct in these areas. When viewed from within the myocardium, the waveforms observed in bipolar intramyocardial electrodes are inconsistent with the dipole layer hypothesis as a model of the electromotive surface of ventricular depolarization in the heart. This investigation was supported in part by U. S. Public Health Service Research Grants HE 09123, HE 10722, and HE 07888 from the National Heart and Lung Institute. ADDITIONAL KEY WORDSReceived October 6, 1967. Accepted for publication August 17, 1970. based embodied the following assumptions: (a) the heart was a distributed set of fixed locus dipoles; (b) the volume conductor was resistive, isotropic, and contained internal inhomogeneities (lungs) and was limited by a normal male adult torso external boundary; (c) the ventricular activation sequence in humans was that reported by Durrer (5) and similar to that recorded in dogs by Scher (6); (d) the wave of depolarization through the ventricles was a current dipole layer; (e) the variation in the velocity of propagation of the wave of depolarization from endocardium to epicardium in the ventricular wall was so minimal that it could be ignored; (f) the electromotive source distribution and strength were always uniform over the entire propagation front.

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