Term
| Phase 1 Ventricular Filling |
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Definition
| During mid-to-late diastole blood returning to the heart via the systemic and pulmonary veins enters the relaxed atria and passes through the AV valves and into the ventricles under its own pressure. Meanwhile the pulmonary and aortic valves are closed. Later in diastole the atria contract, driving more blood into the ventricles. Shortly after, the atria relaxes and systole begins |
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Term
| Phase 2 Isovolumetric Contraction |
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Definition
| Ventricles contract raising ventricular pressure. When ventricular pressure exceeds atrial pressure the AV valves close. No blood flows in or out of the ventricles because all valves are closed. Phase 2 ends when the ventricular pressure is great enough to open the semilunar valves and blood leaves the ventricles. |
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Term
| Phase 3 Ventricular Ejection |
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Definition
| Blood is ejected into the aorta and pulmonary arteries through the open semilunar valve. When ventricular pressure declines below aortic pressure the semilunar valves close ending ejection and marking the beginning of diastole. |
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Term
| Phase 4 Isovolumetic Relaxation |
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Definition
| Ventricular myocardium is relaxing. Some blood is present in the ventricles and it remains unde preessure because it takes time for the tension in the ventricular muscle to wane. All valves are closed. Once ventricular pressure decreases to less than atrial pressure AV valves open again and blood enters the ventricles from the atria. |
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