The ventricular septum is the thick muscular wall that divides the left and right ventricles (the two lower pumping chambers of the heart) from each other. Together with the interatrial septum (which separates the two atria), it forms the internal partitioning of the heart. The ventricular septum comprises the muscular portion (the bulk of the wall, which contracts with each heartbeat) and a smaller membranous portion near the aortic root.
The ventricular septum maintains the separation of the systemic (high-pressure) and pulmonary (lower-pressure) circulations, ensuring oxygenated blood from the left ventricle and deoxygenated blood from the right ventricle are kept separate and directed to their correct destinations. The septal muscle also forms part of the left ventricular contraction itself; when the left ventricle contracts, the septum thickens and moves inwards, contributing to the ejection of blood into the aorta.
The interventricular septum forms part of the cardiac conduction pathway. The bundle of His passes through the membranous septum before dividing into the left and right bundle branches, which course along the septal surface to deliver electrical impulses to their respective ventricles. Damage to the septum from a myocardial infarction can disrupt this conduction system, producing bundle branch block.
A hole in the ventricular septum (ventricular septal defect) is the most common congenital heart defect. Abnormal septal thickening is the hallmark of hypertrophic cardiomyopathy, particularly in the asymmetric form affecting the upper septum. Septal wall motion abnormalities on echocardiography indicate areas of previous myocardial infarction.
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