The Cardiac Cycle

Also called

cardiac cycle · heartbeat · heart beat · heart cycle · systole and diastole · atrial systole · ventricular systole · joint diastole · isovolumetric contraction · isovolumetric relaxation · heart sounds · lub dub · S1 and S2 · heart valves · AV valves · semilunar valves · tricuspid valve · bicuspid valve · mitral valve · aortic valve · pulmonary valve · SA node · sinoatrial node · pacemaker · AV node · atrioventricular node · bundle of His · Purkinje fibres · nodal tissue · conduction system of the heart · ECG · pressure volume · stroke volume · heart rate · cardiac output · Wiggers diagram · body fluids and circulation · double circulation

Topics

• One cardiac cycle = one heartbeat. At 75 beats a minute it lasts 60/75 = 0.8 s.
• The SA node in the right atrium starts each beat; the signal spreads over both atria before they contract (atrial…
• The AV node delays the signal (about 0.1 s here); then the bundle of His…
• Valves are passive: blood pressure pushes them open and shut. A valve opens only when the pressure behind it is higher…
• Most ventricular filling happens passively, with the AV valves open, before the atria contract.
• Isovolumetric contraction: the AV valves have shut (S1), the semilunar valves have not opened yet…
• Ejection: ventricular pressure exceeds aortic and pulmonary pressure, the semilunar valves open and blood leaves…
• Isovolumetric relaxation: the semilunar valves shut (S2), all four valves are shut and pressure falls with no change…
• In this ideal normal cycle the AV and semilunar valves of one ventricle are never open at the same time.
• Left-side pressures (about 120/80 mmHg in the aorta) are much higher than right-side pressures (about 22/12 mmHg in…
• Stroke volume = end-diastolic volume - end-systolic volume (here about 126 - 52 = 74 ml).
• At a faster heart rate each beat is shorter, and most of the time saved comes out of diastole, not systole.

About this model

A GLB file of about 2200 KB, shown in Lably's 3D viewer and, on a phone, placed in your room with AR. Credit: Real heart (outside view): HuBMAP Human Reference Atlas, CCF 3D Reference Object Library (Kristen Browne et al., NIH/NIAID; derived from the NLM Visible Human Project), CC BY 4.0, simplified from 118306 to 8997 triangles. Cut-open heart, valves, vessels, conduction system, gauges, strip and all motion: made for Lably. | CC BY 4.0 (contains a simplified HuBMAP Human Reference Atlas heart mesh, CC BY 4.0). Authored parts by Lably.

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