--- title: "Ventricular Ejection Phase | Anatomy I" description: "Ventricular ejection phase is the cardiac cycle stage when the ventricles contract and push blood into the aorta and pulmonary trunk in Anatomy and Physiology I." canonical: "https://fiveable.me/anatomy-physiology/key-terms/ventricular-ejection-phase" type: "key-term" subject: "Anatomy and Physiology I" unit: "Unit 19" --- # Ventricular Ejection Phase | Anatomy I ## Definition The ventricular ejection phase is the part of the cardiac cycle when the ventricles contract and force blood out of the heart. In Anatomy and Physiology I, it follows ventricular filling and is the main pumping step of systole. ## What It Is The ventricular ejection phase is the part of the cardiac cycle in Anatomy and Physiology I when the ventricles actively push blood out of the heart. Left ventricular contraction sends blood into the aorta, and right ventricular contraction sends blood into the pulmonary trunk and then the pulmonary arteries. This phase begins after the ventricles have filled during diastole and after the pressure inside each ventricle rises enough to open the semilunar valves. The aortic and pulmonary valves do not open just because the heart contracts. They open only when ventricular pressure becomes greater than the pressure in the aorta and pulmonary trunk. That pressure change is the whole point of ejection. Before ejection starts, the ventricles are building force. Once the pressure threshold is crossed, blood moves out quickly along the pressure gradient. As the ventricles keep contracting, blood volume in the chambers drops, which is why this phase is tied to a falling ventricular volume and a rising arterial pressure. The phase does not last forever. It ends when ventricular pressure falls below the pressure in the great arteries. At that point, the semilunar valves close so blood does not flow backward. After that, the heart moves into relaxation and the next filling stage begins. A common mistake is thinking the ventricles eject blood just because they squeeze. In reality, valve movement depends on pressure differences, not a simple open and close command. If the pressure in the ventricle is not high enough, blood stays put. If it becomes high enough, the valves swing open and ejection begins. You can picture it as the heart's main output phase. The atria are not the ones sending blood to the body or lungs here. The ventricles are the chambers doing the work, and the semilunar valves make sure the flow goes forward instead of leaking back into the heart. ## Why It Matters The ventricular ejection phase matters because it is the step that actually drives blood into circulation. Without ejection, the heart could fill normally but never deliver oxygen-rich blood to the body or oxygen-poor blood to the lungs. This is where pressure, valve function, and chamber contraction all come together in one clean sequence. It also connects directly to the rest of the cardiac cycle. If you know when ejection happens, it becomes easier to understand systole versus diastole, the timing of the atrioventricular and semilunar valves, and why pressure changes create one-way flow. That makes it easier to trace heartbeat diagrams and label what each chamber is doing. In A&P I, this term often shows up when you are comparing left and right heart function or interpreting a cardiac cycle chart. The left ventricle has to generate enough pressure to send blood through the systemic circuit, while the right ventricle pumps to the lungs at lower pressure. Ejection is the moment that difference matters most. ## Connections ### Systole Ventricular ejection is a major part of systole, the contraction phase of the cardiac cycle. When you see systole on a diagram or in a question, ejection is the part where contraction is doing the actual pumping work after pressure rises enough to open the semilunar valves. ### Diastole Diastole is the relaxation and filling phase that comes before ventricular ejection. The ventricles fill during diastole, then pressure builds until ejection can begin. If you mix up the two, it gets hard to explain why blood moves out only after the chambers were first filled. ### [Atrioventricular Valves](/anatomy-physiology/key-terms/atrioventricular-valves) The AV valves are closed during ventricular ejection, which keeps blood from moving backward into the atria. Their closing helps separate filling from pumping, so pressure from ventricular contraction goes forward into the great arteries instead of leaking upward. ### [Aortic Valve](/anatomy-physiology/key-terms/aortic-valve) The aortic valve opens during left ventricular ejection when ventricular pressure exceeds aortic pressure. That opening lets blood enter the aorta. If the pressure drops again, the valve closes, which protects against backflow into the left ventricle. ## On the AP Exam A quiz item or lab diagram question may ask you to identify which cardiac phase is happening when the ventricles are contracting and blood is leaving the heart. You might trace the step from ventricular filling to pressure buildup to semilunar valve opening, then explain why flow stops when arterial pressure becomes greater than ventricular pressure again. On a heart cycle chart, this is the phase where ventricular volume falls. In a case question, you may need to connect a weak ejection phase with reduced cardiac output or abnormal valve timing. If the prompt gives you a pressure graph, look for the point where ventricular pressure rises above aortic or pulmonary pressure, because that marks the start of ejection. ## Key Takeaways - The ventricular ejection phase is when the ventricles contract and push blood into the aorta and pulmonary trunk. - It happens after ventricular filling and after pressure inside the ventricles becomes high enough to open the semilunar valves. - Ejection ends when ventricular pressure falls below arterial pressure, which closes the valves and prevents backflow. - This phase is part of systole, not diastole, because the heart is actively pumping blood out. - Pressure changes, not just muscle contraction, determine when blood actually leaves the heart. ## FAQs ### What is ventricular ejection phase in Anatomy and Physiology I? It is the part of the cardiac cycle when the ventricles contract and send blood out of the heart. Left ventricular ejection sends blood into the aorta, and right ventricular ejection sends blood into the pulmonary trunk. The phase ends when the semilunar valves close. ### What happens before ventricular ejection phase? Before ejection, the ventricles fill during diastole and then begin contracting. As contraction raises ventricular pressure, the semilunar valves open only when that pressure becomes greater than the pressure in the aorta or pulmonary trunk. That pressure change is what starts ejection. ### Is ventricular ejection phase part of systole or diastole? It is part of systole. Systole is the contraction phase of the cardiac cycle, and ventricular ejection is the part of systole where contraction results in blood leaving the ventricles. Diastole is the relaxation and filling phase that comes after. ### How do I identify ventricular ejection on a cardiac cycle diagram? Look for the period when ventricular pressure is high, semilunar valves are open, and ventricular volume is decreasing. If a graph shows the ventricle pushing blood into the aorta or pulmonary trunk, that is the ejection phase. It is often followed by valve closure and a drop in pressure. ## Related Study Guides - [19.3 Cardiac Cycle ](/anatomy-physiology/unit-19/3-cardiac-cycle/study-guide/YvRk8a3OeQm0aWtw) ## 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/ventricular-ejection-phase#resource","name":"Ventricular Ejection Phase | Anatomy I","url":"https://fiveable.me/anatomy-physiology/key-terms/ventricular-ejection-phase","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/ventricular-ejection-phase#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:43.193Z","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/ventricular-ejection-phase#term","name":"ventricular ejection phase","description":"The ventricular ejection phase is the part of the cardiac cycle when the ventricles contract and force blood out of the heart. In Anatomy and Physiology I, it follows ventricular filling and is the main pumping step of systole.","url":"https://fiveable.me/anatomy-physiology/key-terms/ventricular-ejection-phase","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 ventricular ejection phase in Anatomy and Physiology I?","acceptedAnswer":{"@type":"Answer","text":"It is the part of the cardiac cycle when the ventricles contract and send blood out of the heart. Left ventricular ejection sends blood into the aorta, and right ventricular ejection sends blood into the pulmonary trunk. The phase ends when the semilunar valves close."}},{"@type":"Question","name":"What happens before ventricular ejection phase?","acceptedAnswer":{"@type":"Answer","text":"Before ejection, the ventricles fill during diastole and then begin contracting. As contraction raises ventricular pressure, the semilunar valves open only when that pressure becomes greater than the pressure in the aorta or pulmonary trunk. That pressure change is what starts ejection."}},{"@type":"Question","name":"Is ventricular ejection phase part of systole or diastole?","acceptedAnswer":{"@type":"Answer","text":"It is part of systole. Systole is the contraction phase of the cardiac cycle, and ventricular ejection is the part of systole where contraction results in blood leaving the ventricles. Diastole is the relaxation and filling phase that comes after."}},{"@type":"Question","name":"How do I identify ventricular ejection on a cardiac cycle diagram?","acceptedAnswer":{"@type":"Answer","text":"Look for the period when ventricular pressure is high, semilunar valves are open, and ventricular volume is decreasing. If a graph shows the ventricle pushing blood into the aorta or pulmonary trunk, that is the ejection phase. It is often followed by valve closure and a drop in pressure."}}]},{"@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":"ventricular ejection phase"}]}]} ```