The excitatory process observed in the exposed human heart

1. A study of the arrival of the excitation process at a number of points on the surface of the human heart with reference to the beginning of R in Lead II was made. It was found that the order of excitation differs in some respects from that found by Lewis and Rothschild in the dog. The earliest points were on the anterior surface of the right ventricle near the atrio-ventricular border. Our results suggest that the conducting tracts in the right ventricle of man may differ from those of the dog. 2. The curves produced by stimulation of various points on the surface of the human heart were recorded in the three standard leads taken simultaneously. These curves indicate that: (a) Ventricular premature contractions of right ventricular origin are represented in the electrocardiogram by ventricular complexes in which the chief initial deflection is upward in Lead I. Ventricular premature contractions of left ventricular origin are represented in the electrocardiogram by ventricular complexes in which the chief initial deflection is downward in Lead I. (b) The clinical electrocardiograms at present ascribed to block in the right branch of the His-bundle indicate block in the left branch, and vice versa. (c) In so-called left ventricular preponderance the electrocardiogram is dominated by right ventricular effects and vice versa.