--- title: "Bicuspid Valve | General Biology I" description: "Bicuspid valve is the left atrioventricular valve that keeps blood moving from the left atrium to the left ventricle and prevents backflow in General Biology I." canonical: "https://fiveable.me/college-bio/key-terms/bicuspid-valve" type: "key-term" subject: "General Biology I" unit: "Unit 40" --- # Bicuspid Valve | General Biology I ## Definition The bicuspid valve, also called the mitral valve, is the left atrioventricular valve in the heart. It lets blood move from the left atrium into the left ventricle and stops backflow when the ventricle contracts. ## What It Is The bicuspid valve is the two-flap valve between the left atrium and left ventricle in the mammalian heart. In General Biology I, you usually see it as part of the heart’s one-way flow system, where each valve opens and closes in response to pressure changes during the cardiac cycle. It opens when pressure in the left atrium is higher than pressure in the left ventricle, which lets oxygen-rich blood flow into the ventricle. That filling happens before the ventricle contracts. Once the left ventricle starts squeezing, pressure rises fast and the valve closes so blood does not leak backward into the atrium. The term bicuspid refers to the two leaflets, or cusps, that make up the valve. Many classes also call it the mitral valve because its shape resembles a bishop’s mitre. You do not need to memorize the nickname to understand the job, but you do need to know that bicuspid and mitral valve name the same structure. The valve does not work alone. Thin connective tissue cords, called chordae tendineae, help anchor the leaflets so they do not flip inside out during ventricular contraction. Those cords are attached to papillary muscles in the ventricle, which tighten at the right time to stabilize the valve. That arrangement is a neat example of how structure supports function in biology. A common mistake is thinking valves actively pump blood. They do not. Blood pressure differences do the moving, and the valve simply responds by opening or closing at the right moment. If the bicuspid valve does not close well, blood can flow backward, which is called regurgitation. If the leaflets bulge into the left atrium, that is mitral valve prolapse, a condition that shows up when the valve’s normal one-way function is disrupted. ## Why It Matters The bicuspid valve shows how the heart keeps blood moving in a single direction, which is a core idea in mammalian circulatory anatomy. If you understand this valve, it becomes easier to trace the path of blood through the heart and explain why the left side has to handle higher pressure than the right side. It also connects structure to function in a very direct way. The two leaflets, the chordae tendineae, and the papillary muscles all work together so the valve closes without flipping backward when the ventricle contracts. That is a good example of how Biology I asks you to connect parts of an organ to what the organ actually does. This term also helps when you compare the bicuspid valve with the other heart valves. The tricuspid valve sits on the right side, while the aortic and pulmonary valves control blood leaving the ventricles. Knowing which valve is where makes heart diagrams and circulation questions much easier to interpret. ## Connections ### Tricuspid Valve The tricuspid valve is the matching atrioventricular valve on the right side of the heart. Comparing it with the bicuspid valve helps you keep the heart’s right and left sides straight. Both valves open to let blood enter a ventricle and close when the ventricle contracts, but they serve different chambers and handle different pressure levels. ### [Aortic Valve](/college-bio/key-terms/aortic-valve) The aortic valve sits after the left ventricle and controls blood entering the aorta. The bicuspid valve is upstream of it, so blood passes through the bicuspid valve first, then the aortic valve when the left ventricle ejects blood. If you trace flow through the left side of the heart, these two valves appear in sequence. ### [Atrioventricular Valve](/college-bio/key-terms/atrioventricular-valve) The bicuspid valve is one example of an atrioventricular valve, which means it lies between an atrium and a ventricle. This category matters because atrioventricular valves are built to stop backflow during ventricular contraction. The bicuspid valve and tricuspid valve are the two atrioventricular valves in the mammalian heart. ### [cardiac cycle](/college-bio/key-terms/cardiac-cycle) The bicuspid valve opens and closes at specific points in the cardiac cycle. It opens during ventricular filling, then closes during ventricular systole when pressure in the ventricle rises. If you are labeling heart events in order, the valve’s movement helps you connect pressure changes to blood flow. ## On the AP Exam A quiz question might ask you to label a heart diagram, trace blood flow, or explain why the left atrium does not empty backward when the left ventricle contracts. In those problems, you use the bicuspid valve as a checkpoint in the flow path: blood moves from the left atrium through the bicuspid valve into the left ventricle, then the valve closes during contraction. If you see a description of valve failure, connect it to regurgitation or mitral valve prolapse. In lab or lecture questions, you may also be asked to compare the bicuspid valve with the tricuspid, aortic, or pulmonary valve and say whether it is an atrioventricular valve or a semilunar valve. ## bicuspid valve vs Tricuspid Valve These two are easy to mix up because they are both atrioventricular valves, but they are on opposite sides of the heart. The bicuspid valve is on the left and has two leaflets, while the tricuspid valve is on the right and has three leaflets. If a question mentions oxygen-rich blood leaving the left atrium, it is pointing to the bicuspid valve. ## Key Takeaways - The bicuspid valve is the left atrioventricular valve, located between the left atrium and left ventricle. - It has two leaflets and closes during ventricular contraction to stop blood from flowing backward into the left atrium. - Blood pressure, not the valve itself, drives opening and closing during the cardiac cycle. - Chordae tendineae and papillary muscles help keep the valve from inverting when pressure rises in the ventricle. - If the valve does not close properly, blood can leak backward, which is called regurgitation. ## FAQs ### What is the bicuspid valve in General Biology I? The bicuspid valve is the valve between the left atrium and left ventricle of the heart. It lets blood move forward into the ventricle and prevents backflow when the ventricle contracts. You may also see it called the mitral valve. ### Is the bicuspid valve the same as the mitral valve? Yes, bicuspid valve and mitral valve are two names for the same structure. "Bicuspid" describes the two leaflets, while "mitral" refers to its shape. In Biology I, either term can appear on a diagram or test question. ### How does the bicuspid valve prevent backflow? When the left ventricle contracts, pressure inside the ventricle rises above pressure in the left atrium. That pressure change forces the bicuspid valve shut. The chordae tendineae and papillary muscles help keep the leaflets from flipping backward. ### What happens if the bicuspid valve does not work correctly? If the valve does not close tightly, blood can leak back into the left atrium, which is called regurgitation. A common related condition is mitral valve prolapse, where the valve leaflets bulge the wrong way during contraction. Both change the normal one-way flow of blood. ## 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/bicuspid-valve#resource","name":"Bicuspid Valve | General Biology I","url":"https://fiveable.me/college-bio/key-terms/bicuspid-valve","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/college-bio/key-terms/bicuspid-valve#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"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/college-bio/key-terms/bicuspid-valve#term","name":"bicuspid valve","description":"The bicuspid valve, also called the mitral valve, is the left atrioventricular valve in the heart. 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