---
title: "Atrioventricular Septum | Anatomy and Physiology I"
description: "Atrioventricular septum is the embryonic partition between atria and ventricles, formed by endocardial cushion fusion in Anatomy and Physiology I."
canonical: "https://fiveable.me/anatomy-physiology/key-terms/atrioventricular-septum"
type: "key-term"
subject: "Anatomy and Physiology I"
unit: "Unit 19"
---

# Atrioventricular Septum | Anatomy and Physiology I

## Definition

The atrioventricular septum is the embryonic tissue that helps separate the atria from the ventricles. In Anatomy and Physiology I, it matters because errors in its formation can cause congenital heart defects and rhythm problems.

## What It Is

The atrioventricular septum is the part of the developing heart that helps divide the upper chambers, the atria, from the lower chambers, the ventricles. In Anatomy and Physiology I, you usually meet it while tracing how the simple embryonic heart tube becomes a four-chambered heart during the first eight weeks of development.

It forms from the endocardial cushions, thickened areas of tissue that grow inside the primitive heart tube. Around the fourth week of embryonic development, these cushions merge and help build the central partition between the atria and ventricles. That fusion is part of cardiac septation, the overall process that shapes the heart into separate right and left sides.

This partition does more than create a wall. It also helps organize blood flow so oxygen-poor blood on the right side and oxygen-rich blood on the left side stay separated after birth. Before birth, fetal circulation is different because the fetus gets oxygen from the placenta, but the basic heart layout still has to form correctly so the newborn heart can pump efficiently right away.

The atrioventricular septum is closely tied to the atrioventricular cushions and the atrioventricular node. The cushions contribute to the structure, while the node sits in this region and helps carry electrical signals from the atria to the ventricles. That means this area is part of both the heart’s anatomy and its conduction system.

If the septum does not form correctly, the result can be an atrioventricular septal defect. That kind of defect can leave abnormal openings between chambers or distort the valves and septal walls. In a class setting, this usually comes up when you are matching embryonic structures to adult anatomy, or when you are tracing how a small developmental mistake leads to a bigger functional problem.

## Why It Matters

The atrioventricular septum is one of the best examples of how structure and function are linked in Anatomy and Physiology I. If this region develops normally, the heart can separate chamber functions, route blood in the right direction, and coordinate electrical signaling between atria and ventricles.

This term also helps you make sense of congenital heart defects. When you see a case about an infant with abnormal mixing of blood, a murmur, or a problem involving the septa or valves, the atrioventricular septum may be part of the explanation. Instead of memorizing defects as isolated names, you can connect them to the embryology behind them.

It also reinforces a big course idea: organs do not appear fully formed all at once. The heart starts as a tube, then folds, septates, and matures through a series of developmental steps. The atrioventricular septum is one of the landmarks in that timeline, so it is useful for quizzes, labeling diagrams, and short-answer explanations about heart development.

## Connections

### Endocardial Cushions

These are the tissue swellings that fuse to help form the atrioventricular septum. If you know what the cushions do, the septum makes more sense as a product of growth and fusion rather than a structure that simply appears. They also contribute to parts of the heart valves, so they matter beyond just one partition.

### Cardiac Septation

Cardiac septation is the larger process that splits the primitive heart into separate chambers. The atrioventricular septum is one piece of that bigger developmental sequence. When you study septation, you are tracking how the atria, ventricles, and outflow tracts each become distinct structures.

### [Atrial Septum](/anatomy-physiology/key-terms/atrial-septum)

The atrial septum separates the two atria, while the atrioventricular septum sits lower and helps divide the atria from the ventricles. These are easy to mix up because both are part of heart partitioning. Comparing them side by side helps you place each structure on a heart diagram correctly.

### [Interventricular Septum](/anatomy-physiology/key-terms/interventricular-septum)

This septum separates the right and left ventricles, so it works at a different level than the atrioventricular septum. The two structures are often discussed together because both are part of the heart’s internal walls. If one is missing or incomplete, blood can mix or chamber pressures can be affected.

## On the AP Exam

A quiz question on the atrioventricular septum usually asks you to identify where it forms, what embryonic tissue builds it, or what defect results if development goes wrong. In a diagram label, you may need to place it between the atria and ventricles and distinguish it from the atrial or interventricular septum. If your instructor uses case studies, you might read about abnormal blood mixing, a murmur, or a congenital septal defect and trace the problem back to failed endocardial cushion fusion. A short-answer question may ask you to explain how one early developmental error changes both heart structure and function.

## atrioventricular septum vs Atrial Septum

The atrial septum separates the right and left atria, while the atrioventricular septum helps separate the atria from the ventricles. They are both part of heart septation, but they sit in different places and have different jobs. If you are labeling a heart diagram, the atrial septum is the wall between the upper chambers, not the central junction where atria meet ventricles.

## Key Takeaways

- The atrioventricular septum is a developing heart structure that helps separate the atria from the ventricles.
- It forms from fused endocardial cushions during early embryonic development, around the fourth week.
- This region matters because it supports proper chamber separation and normal blood flow in the finished heart.
- The atrioventricular septum is linked to the atrioventricular node, so it is relevant to both anatomy and electrical conduction.
- Problems in this area can lead to congenital heart defects, especially atrioventricular septal defects.

## FAQs

### What is atrioventricular septum in Anatomy and Physiology I?

It is the embryonic tissue region that helps divide the atria from the ventricles. In A&P I, you study it as part of heart development and cardiac septation. It forms from endocardial cushions and helps set up the normal chamber layout of the heart.

### What forms the atrioventricular septum?

The atrioventricular septum forms from the fusion of the endocardial cushions. These cushions are thickened areas in the early heart that grow together as the heart partitions into separate chambers. If that fusion is incomplete, the heart can develop structural defects.

### How is the atrioventricular septum different from the interventricular septum?

The atrioventricular septum is higher up in the heart and separates the atria from the ventricles. The interventricular septum runs between the two ventricles. They are both septa, but they divide different chamber pairs and are formed during different parts of heart development.

### What happens if the atrioventricular septum does not develop correctly?

A defect can leave openings or abnormal connections between chambers, leading to an atrioventricular septal defect. That can affect blood flow and may also disturb the nearby conduction system. In class, this often shows up in questions about congenital heart disease and embryology.

## Related Study Guides

- [19.1 Heart Anatomy ](/anatomy-physiology/unit-19/1-heart-anatomy/study-guide/rkGmPKJ0SjTIT3Kf)

## About This Document

Canonical Fiveable pages are available as Markdown at the same path plus `.md`.

- [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns
- [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing
- [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`)
- [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`)

## Structured Data

```json
{"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/anatomy-physiology/key-terms/atrioventricular-septum#resource","name":"Atrioventricular Septum | Anatomy and Physiology I","url":"https://fiveable.me/anatomy-physiology/key-terms/atrioventricular-septum","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/atrioventricular-septum#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:36.800Z","isPartOf":{"@type":"Collection","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/anatomy-physiology/key-terms/atrioventricular-septum#term","name":"atrioventricular septum","description":"The atrioventricular septum is the embryonic tissue that helps separate the atria from the ventricles. In Anatomy and Physiology I, it matters because errors in its formation can cause congenital heart defects and rhythm problems.","url":"https://fiveable.me/anatomy-physiology/key-terms/atrioventricular-septum","inDefinedTermSet":{"@type":"DefinedTermSet","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"}},{"@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What is atrioventricular septum in Anatomy and Physiology I?","acceptedAnswer":{"@type":"Answer","text":"It is the embryonic tissue region that helps divide the atria from the ventricles. In A&P I, you study it as part of heart development and cardiac septation. It forms from endocardial cushions and helps set up the normal chamber layout of the heart."}},{"@type":"Question","name":"What forms the atrioventricular septum?","acceptedAnswer":{"@type":"Answer","text":"The atrioventricular septum forms from the fusion of the endocardial cushions. These cushions are thickened areas in the early heart that grow together as the heart partitions into separate chambers. If that fusion is incomplete, the heart can develop structural defects."}},{"@type":"Question","name":"How is the atrioventricular septum different from the interventricular septum?","acceptedAnswer":{"@type":"Answer","text":"The atrioventricular septum is higher up in the heart and separates the atria from the ventricles. The interventricular septum runs between the two ventricles. They are both septa, but they divide different chamber pairs and are formed during different parts of heart development."}},{"@type":"Question","name":"What happens if the atrioventricular septum does not develop correctly?","acceptedAnswer":{"@type":"Answer","text":"A defect can leave openings or abnormal connections between chambers, leading to an atrioventricular septal defect. That can affect blood flow and may also disturb the nearby conduction system. In class, this often shows up in questions about congenital heart disease and embryology."}}]},{"@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Anatomy and Physiology I","item":"https://fiveable.me/anatomy-physiology"},{"@type":"ListItem","position":2,"name":"Key Terms","item":"https://fiveable.me/anatomy-physiology/key-terms"},{"@type":"ListItem","position":3,"name":"Unit 19","item":"https://fiveable.me/anatomy-physiology/unit-19"},{"@type":"ListItem","position":4,"name":"atrioventricular septum"}]}]}
```