The heart is a four-chambered muscular pump internally divided by partitions called septa. The interventricular septum (IVS) is a sturdy wall of cardiac tissue that separates the heart’s two lower chambers, the ventricles. This separation is necessary for maintaining the precise flow and pressure required for the pulmonary and systemic circulatory systems.
Precise Location Within the Heart
The interventricular septum is located centrally, directly separating the right ventricle (RV) from the left ventricle (LV). This muscular wall extends from the heart’s base down to the apex. The septum is not positioned vertically but runs obliquely, or diagonally, from the front toward the back of the heart.
This angled placement dictates the overall shape of the ventricles. The septum is curved, with its convex side bulging slightly into the right ventricular chamber. Due to its muscular thickness, the septum forms a substantial part of the left ventricle’s wall, the chamber responsible for pumping blood to the entire body. The margins of the septum on the heart’s outer surface correspond to the anterior and posterior interventricular grooves.
Structure and Primary Physiological Function
The interventricular septum is divided into two distinct parts: a large muscular section and a smaller membranous section. The muscular portion makes up 80 to 90% of the septum’s total mass and is thick, similar to the left ventricular wall. This tissue extends from the apex upward toward the heart’s base.
The membranous portion is a small, thin, fibrous sheet located in the uppermost part of the septum, near the heart’s valves. This section measures only one to two millimeters in thickness.
The primary function of the septum is to prevent oxygen-rich blood in the left ventricle from mixing with deoxygenated blood in the right ventricle. It maintains the significant pressure difference between the two ventricles. The left ventricle generates much higher pressure for systemic circulation, while the right ventricle maintains lower pressure for the trip to the lungs.
Specialized conducting nerve fibers run through the septum, forming part of the heart’s electrical wiring system. These fibers allow the electrical signal to travel from the atria to the ventricles, ensuring coordinated muscular contraction during each heartbeat.
When the Septum is Compromised (Clinical Relevance)
A Ventricular Septal Defect (VSD) occurs when the septum develops with an opening. As one of the most common congenital heart defects, VSDs are present at birth, often located in the membranous portion of the septum.
The hole allows blood to shunt, or flow abnormally, between the two ventricles. Because the left ventricle operates at a much higher pressure, blood typically flows from the high-pressure left side to the lower-pressure right side. This extra blood volume travels to the lungs, forcing the heart and lungs to work harder.
The severity of a VSD depends on the size of the opening. Small defects may close spontaneously, often within the first year of life, requiring only monitoring. Larger defects can lead to serious complications, such as heart failure.
Treatment for larger or symptomatic VSDs often involves surgical closure using stitches or a synthetic patch, or a less invasive catheter-based procedure.