--- title: "Atrioventricular Node | General Biology I" description: "Atrioventricular node is the heart’s electrical relay that delays impulses so atria empty before ventricles contract in General Biology I." canonical: "https://fiveable.me/college-bio/key-terms/atrioventricular-node" type: "key-term" subject: "General Biology I" unit: "Unit 40" --- # Atrioventricular Node | General Biology I ## Definition The atrioventricular node (AV node) is a cluster of specialized heart cells that briefly delays the electrical signal between the atria and ventricles. In General Biology I, it explains how the heart keeps blood moving in the right order. ## What It Is The atrioventricular node, or AV node, is a small patch of specialized cardiac tissue in General Biology I that sits at the junction between the atria and ventricles. It receives the electrical impulse that starts in the sinoatrial node and passes that signal along to the lower chambers of the heart, but not instantly. That short pause is the whole point. The AV node slows the signal by about a tenth of a second, giving the atria time to finish contracting and push blood into the ventricles before the ventricles squeeze. If the lower chambers contracted too early, the heart would waste a lot of each beat. This delay is easy to miss when you first learn the conduction system, because it is not a dramatic muscle movement or a visible valve opening. It is an electrical checkpoint. The AV node acts like a gatekeeper, making sure the timing of the cardiac cycle stays coordinated with the physical movement of blood. After the signal leaves the AV node, it travels through the Bundle of His and then through the rest of the conduction pathway to trigger ventricular contraction. That sequence matters because the ventricles do the strong pumping work that sends blood to the lungs and the rest of the body. The AV node helps make sure that pump is filled before it fires. The AV node can also generate its own electrical impulses if the sinoatrial node fails, but it does this more slowly. That backup ability keeps the heart beating, though the rhythm may be less efficient. In biology terms, this is a good example of how form and function are linked, the structure is built not just to transmit signals, but to protect timing and maintain circulation. ## Why It Matters The AV node matters because it connects heart anatomy to the rhythm of the cardiac cycle. When you trace how blood moves through the heart, the AV node is the step that makes atrial contraction happen before ventricular contraction, which keeps filling and pumping coordinated. This term also helps you explain what goes wrong in heart block. If the signal is delayed too much or blocked at the AV node, the atria and ventricles stop working in sync, and the heart becomes less efficient at moving blood. That is why this tiny cluster of cells shows up in discussions of arrhythmias and conduction problems. In General Biology I, the AV node is a good checkpoint term for labs, diagrams, and short-answer questions about the mammalian heart. If you can trace the pathway from the sinoatrial node to the AV node to the Bundle of His, you can usually explain both normal heartbeat timing and several abnormal cases. ## Connections ### [Sinoatrial Node](/college-bio/key-terms/sinoatrial-node) The sinoatrial node starts the heartbeat, while the AV node receives that signal and delays it. If you confuse the two, check the direction of flow: the SA node is the pacemaker in the upper heart, and the AV node is the timing checkpoint between atria and ventricles. ### Bundle of His The Bundle of His carries the electrical signal away from the AV node into the ventricles. In a pathway question, the AV node comes first, then the Bundle of His, then the signal spreads through the lower chambers to trigger contraction. ### [Cardiac Cycle](/college-bio/key-terms/cardiac-cycle) The AV node makes the cardiac cycle work in the correct sequence. Its delay lets atrial systole finish before ventricular systole begins, so you can connect electrical conduction with the pressure and volume changes in the heart beat. ### [Cardiac muscle](/college-bio/key-terms/cardiac-muscle) Cardiac muscle is the tissue that contracts when the conduction system sends a signal. The AV node does not pump blood itself, but it coordinates when cardiac muscle in the atria and ventricles contracts, which is why it belongs in the same topic. ## On the AP Exam A diagram label or short-answer question may ask you to place the AV node in the heart’s conduction pathway and explain why the delay matters. The move is to trace the signal in order, starting at the sinoatrial node, then the AV node, then the Bundle of His and the ventricles. If a question describes atria and ventricles contracting out of sync, the AV node is one of the first structures you should suspect. In a case question about heart block, you may need to explain that the conduction delay becomes too long or fails, which lowers pumping efficiency. ## atrioventricular node vs Sinoatrial Node These two nodes are easy to mix up because both are part of the heart’s conduction system. The sinoatrial node starts the impulse, while the atrioventricular node delays and relays it to the ventricles. A simple memory trick is that the SA node sets the pace and the AV node times the handoff. ## Key Takeaways - The atrioventricular node is a cluster of specialized cells that sits between the atria and ventricles of the heart. - Its main job is to delay the electrical signal long enough for the atria to empty blood into the ventricles. - That delay keeps the cardiac cycle coordinated, so the ventricles fill before they contract. - If the SA node fails, the AV node can act as a slower backup pacemaker. - Problems at the AV node can lead to heart block and inefficient blood flow. ## FAQs ### What is atrioventricular node in General Biology I? The atrioventricular node is a specialized group of heart cells that slows the electrical impulse between the atria and ventricles. In the mammalian heart, that pause keeps the chambers contracting in the right order so blood moves efficiently. ### What does the AV node do during the cardiac cycle? It creates a short delay after the atria receive the electrical signal from the sinoatrial node. That delay gives the ventricles time to fill before they contract, which makes each heartbeat more effective. ### How is the AV node different from the sinoatrial node? The sinoatrial node starts the heartbeat, so it acts like the main pacemaker. The AV node receives that signal, pauses it briefly, and then passes it on to the ventricles. ### What happens if the AV node does not work properly? The heart may develop a block in signal conduction, which can slow or disrupt the timing between atrial and ventricular contraction. That can reduce how well the heart pumps blood, especially if the ventricles are not filling and contracting in sync. ## Related Study Guides - [40.3 Mammalian Heart and Blood Vessels](/college-bio/unit-40/3-mammalian-heart-blood-vessels/study-guide/JlPxEHJvSF7RtGKG) ## 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/college-bio/key-terms/atrioventricular-node#resource","name":"Atrioventricular Node | General Biology I","url":"https://fiveable.me/college-bio/key-terms/atrioventricular-node","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/college-bio/key-terms/atrioventricular-node#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:21:07.934Z","isPartOf":{"@type":"Collection","name":"General Biology I Key Terms","url":"https://fiveable.me/college-bio/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/college-bio/key-terms/atrioventricular-node#term","name":"atrioventricular node","description":"The atrioventricular node (AV node) is a cluster of specialized heart cells that briefly delays the electrical signal between the atria and ventricles. 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