Review of Medical Physiology - William F. Ganong 2002

Cardiovascular System
The Nature of the Heartbeat and Electrical Activity of the Heart
Introduction

Normally, the Chambers of the Heart contract in a specific sequence. First, the atria contract (atrial systole), followed by the ventricles (ventricular systole). During diastole, all four chambers of The Heart are relaxed. Heart contraction is triggered by electrical impulses that originate in the specialized Conduction system of the Heart and spread to all PARTS OF THE myocardium. The conduction system consists of the sinoatrial node (SA node), internodal atrial pathways, atrioventricular node (AV node), bundle of His and its branches, and Purkinje fibers. Various parts of the heart's conduction system, and under pathological conditions also areas of the myocardium, are capable of spontaneous impulse generation. Normally, the SA node generates impulses at the highest frequency. These impulses reach other regions before spontaneous depolarization can occur there. Consequently, the SA node serves as the natural pacemaker of the heart. The rate of impulse generation within it determines the heart rate. Impulses originating in the SA node propagate via the atrial pathways to the AV node, and through it to the bundle of His, the bundle branches, and the Purkinje fibers to the ventricular myocardium.



Last update: 10/08/2026

Editorial and Educational Adaptation: This material has been compiled based on the primary/original source text. The project team performed an editorial review, corrected technical inaccuracies, structured sections, and adapted the content for an educational format.

What was processed:

  • elimination of formatting defects (OCR errors, structural breaks, corrupted characters);
  • editorial organization of content;
  • standardization of terminology in accordance with academic sources;
  • verification of factual statements against the original source text.

All mentions of the author, publication year, and origin of the primary text have been preserved in accordance with the source.