The interventricular septum separates the heart’s two ventricles and plays a vital role in maintaining correct bloodflow. Sometimes a defect can occur or be present from birth. This can increase the risk of clotting, arrhythmias, and other problems.

The heart has two upper chambers, the atria, and two lower chambers, the ventricles. A thin, muscular sheet of tissue called the interventricular or ventricular septum divides the two ventricles.

The intraventricular septum plays an important role in the proper functioning of the heart. It helps direct blood flow properly and forms part of the organ’s electrical conduction system. The interventricular septum must be in the correct place for the heart to function correctly.

This article looks at the interventricular septum, its function in the heart, and how it develops in the fetus.

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The interventricular septum is the muscular wall separating the right and left ventricles of the heart. It runs between the interventricular grooves, which are shallow depressions on the surface of the heart.

The interventricular septum is a triangular wall of cardiac tissue that comprises muscular and membranous tissue. The muscular portion consists of the inlet septum, trabecular septum, and infundibular septum. It receives blood from the left coronary artery.

The upper area of the interventricular septum consists primarily of membranous tissue and is much smaller than the lower muscular portion. It usually receives blood from the right coronary artery.

The interventricular septum ensures that blood flows properly through the heart. It flows from the right atrium, into the right ventricle through the tricuspid valve, and then to the lungs. It then returns through the left atrium and into the left ventricle through the mitral valve.

As the heart beats, it pumps blood out during the systole phase. At this point, the interventricular septum becomes shorter and thicker. It also shifts toward the left side of the heart and supports the right ventricle.

During the diastolic phase, the ventricles fill with blood. As a result, the interventricular septum lengthens and moves toward the right ventricle.

These movements help maintain blood flow through the heart and ensure that the ventricles fill correctly.

The interventricular septum also plays an important role in the heart’s electrical conduction system. This system helps coordinate the contraction of the heart muscles. The electrical impulses from the atrioventricular node travel through the Purkinje fibers in the interventricular septum to reach their target.

The heart starts to form early in embryonic development. It begins as a simple tube that grows and becomes more defined as cells in the embryo start to specialize.

Firstly, the tube bends and twists backward into an S shape to begin forming the four chambers. The bottom of the tube moves up and toward the back, eventually forming the atria. The center of the tube first forms a single ventricle, which then divides into two.

The walls of the ventricles begin to expand by around week 4 of embryonic development, forming the interventricular septum. The four heart chambers form by the end of week 7.

However, congenital heart abnormalities may occur if the heart does not twist or divide normally.

Doctors can measure the thickness of the interventricular septum with an echocardiogram. They take the measurement at the end of the diastole phase as the heart relaxes. Doctors may also use a cardiac MRI, as this test is a more sensitive method of imaging the interventricular septum than an echocardiogram.

Limited data is available regarding standard measurements across the age groups.

However, in one 2021 study of 161 healthy children and adolescents aged 6 to 18, researchers found the measurement average to be 5.5 millimeters (mm), with a range of between 4.3 and 6.7 mm.

Several heart abnormalities can affect the interventricular septum.

Ventricular septal defect (VSD)

VSD is a hole in the interventricular septum. It develops as the septum in the developing fetus does not form properly. A VSD can also occur after a heart attack that affects blood flow to the interventricular septum.

In a VSD, blood can flow from the left ventricle through the hole in the septum to the right ventricle and into the lungs. The additional blood pumped to the lungs forces the heart and lungs to work harder. This can lead to:

A VSD can cause holes in various places in the septum. Doctors may use the following names to describe these issues:

  • Conoventricular ventricular septal defect: A hole in the septum under the pulmonary and aortic valves.
  • Perimembranous ventricular septal defect: A hole in the upper ventricular septum.
  • Inlet ventricular septal defect: A hole near where blood enters the ventricles through the tricuspid and mitral valves.
  • Muscular ventricular septal defect: A hole in the lower, muscular part of the ventricular septum.

Treatment depends on the size of the hole and the person’s symptoms. If the hole is small and causes no problems, doctors may leave it to close on its own and monitor the infant closely.

If the hole is larger or does not close on its own, a doctor may recommend either cardiac catheterization or open-heart surgery to close the hole and restore typical blood flow.

Sigmoid septum

A sigmoid septum is a type of heart abnormality that tends to affect older adults. It means that the interventricular septum has an S-shaped contour.

Doctors are unsure of its clinical significance and may consider it a typical part of the aging process that causes no problems. However, certain people may experience shortness of breath or heart arrhythmias, which refer to an atypical heart rhythm.

Interventricular septal aneurysm

An interventricular septal aneurysm is a ballooning of the interventricular septum. It is a rare condition — doctors associate it with 0.3% of congenital heart disease and 19% of VSDs.

Often, it causes no symptoms but may also lead to ventricular obstruction, rupture, blood clots, and electrical conduction abnormalities.

Treatment may include beta-blockers, aspirin, or other blood-thinning medications to prevent clotting.

Atypical septal motion

In some cases, the interventricular septum may move atypically. Doctors call this paradoxical septal motion or bounce. It may develop in people with heart failure or other conditions. It can also occur due to electrical abnormalities in the heart or after heart surgery.

Treatment for this condition may depend on the cause and could include medications or surgery.

The interventricular septum is a muscular wall that divides the heart’s ventricles, or lower chambers, into left and right halves. It helps the blood flow in the correct direction through the heart and has a role in electrical conduction.

Several heart abnormalities can affect the interventricular septum, including VSD, sigmoid septum, and interventricular septal aneurysm. A person may require medications or surgery to correct these issues.