[Direct recording of the electrical activity of the sinoatrial node]

The electrical activity of the sinoatrial node was recorded simultaneously from the epicardial and endocardial surfaces of the sinoatrial node in 73 dogs. The electrical activity of sinoatrial node had the form of a slow deflection and a rapid preatrial deflection, the duration of the former being 81 +/- 28 msec and reflecting slow propagation of excitation within the sinus node. Duration of the rapid preatrial deflection was 17 +/- 11 msec. It reflects the rapid propagation of the sinus impulse (probably, the rapid spread of the excitation in corona of the sinus node and invasion in crista terminals). The form and duration of the slow and rapid deflections changed under the influence of drugs.