Cardiac cycle - wikipedia Cardiac cycle This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( August 2012 ) The circular diagram depicts one heartbeat of the continuously repeating cardiac cycle, namely : ventricular diastole followed by ventricular systole, etc. -- while coordinating with atrial systole followed by atrial diastole, etc. The cycle also correlates to key electrocardiogram tracings : the T wave ( which indicates ventricular diastole ) ; the P wave ( atrial systole ) ; and the QRS ' spikes ' complex ( ventricular systole ) -- all shown as color purple - in - black segments. The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods : one during which the heart muscle relaxes and refills with blood, called diastole ( die - ASS - toe - lee ), followed by a period of robust contraction and pumping of blood, dubbed systole ( SIS - toe - lee ). After emptying, the heart immediately relaxes and expands to receive another influx of blood returning from the lungs and other systems of the body -- before again contracting to pump blood to the lungs and those systems. A normally performing heart must be fully expanded before it can efficiently pump again. Assuming a healthy heart and a typical rate of 70 to 75 beats per minute, each cardiac cycle, or heartbeat, takes about 0.8 second. There are two atrial and two ventricle chambers of the heart ; they are paired as the left heart and the right heart -- that is, the left atrium with the left ventricle, the right atrium with the right ventricle -- and they work in concert to traverse the cardiac cycle continuously, ( see circular diagram at right margin ). At the `` Start '' of the cycle, during ventricular diastole -- early, the heart relaxes and expands while receiving blood into both ventricles through both atria ; then, near the end of ventricular diastole -- late, the two atria begin to contract ( atrial systole ), and each atrium pumps blood into the ventricle ' below ' it. During ventricular systole the ventricles are contracting and vigorously pulsing ( or ejecting ) two separated blood supplies from the heart -- one to the lungs and one to all other body organs and systems -- while the two atria are relaxed ( atrial diastole ). This coordination ensures that blood is efficiently collected and circulated throughout the body. The mitral and tricuspid valves, also known as the atrioventricular, or AV valves, open during ventricular diastole to permit filling. Late in the filling period the atria begin to contract ( atrial systole ) forcing a final crop of blood into the ventricles under pressure -- see circular diagram. Then, prompted by electrical signals from the sinoatrial node, the ventricles start contracting ( ventricular systole ), and as back - pressure against them increases the AV valves are forced to close, which stops the blood volumes in the ventricles from flowing in or out ; this is known as the isovolumic contraction stage. Due to the contractions of the systole, pressures in the ventricles rise quickly, exceeding the pressures in the trunks of the aorta and the pulmonary arteries and causing the requisite valves ( the aortic and pulmonary valves ) to open -- which results in separated blood volumes being ejected from the two ventricles. This is the ejection stage of the cardiac cycle ; it is depicted ( see circular diagram ) as the ventricular systole -- first phase followed by the ventricular systole -- second phase. After ventricular pressures fall below their peak ( s ) and below those in the trunks of the aorta and pulmonary arteries, the aortic and pulmonary valves close again -- see, at right margin, Wiggers diagram, blue - line tracing. Now follows the isovolumic relaxation, during which pressure within the ventricles begin to fall significantly, and thereafter the atria begin refilling as blood returns to flow into the right atrium ( from the vena cavae ) and the left atrium ( from tahe pulmonary veins ). As the ventricles begin to relax, the mitral and tricuspid valves open again, and the completed cycle returns to ventricular diastole and a new `` Start '' of the cardiac cycle. Throughout the cardiac cycle, blood pressure increases and decreases. The movements of cardiac muscle are coordinated by a series of electrical impulses produced by specialised pacemaker cells found within the sinoatrial node and the atrioventricular node. Cardiac muscle is composed of myocytes which initiate their internal contractions without applying to external nerves -- with the exception of changes in the heart rate due to metabolic demand. Contents 1 Cardiac cycle and Wiggers diagram 1.1 Stages 2 Physiology 2.1 Rhythmical conduction 2.2 Heart Conducting System 3 Atrial systole 3.1 Detection 4 Ventricular systole 4.1 Detection 4.1. 1 Heart sounds 4.1. 2 Electrocardiogram 5 Diastole 6 See also 7 References 8 External links Cardiac cycle and Wiggers diagram A Wiggers diagram illustrate events and details of the cardiac cycle with electrographic trace lines, which depict ( vertical ) changes in a parameter 's value as time elapses left - to - right. The ventricular `` Diastole '', or relaxation, begins with `` Isovolumic relaxation '', then proceeds through three sub-stages of inflow, namely : `` Rapid inflow '', `` Diastasis '', and `` Atrial systole ''. ( During the `` Diastole '' period, the `` Ventricular volume '' increases ( see red - line tracing ), beginning after the vertical bar at `` Aortic valve closes '' and ending with the vertical bar at R in the QRS complex ). + The ventricular `` Systole '', or contraction, begins with `` Isovolumic contraction '', i.e., with the vertical bar at `` A - V valve closes '' ; it ends with completing the `` Ejection '' stage at the bar at `` Aortic valve closes ''. During `` Ejection '' stage, the ( red - line ) tracing of `` Ventricular volume '' falls to its least amount ( see ejection fraction ) as the ventricles pump blood to the pulmonary arteries and to the aorta. The cardiac cycle involves four major stages of activity : 1 ) `` Isovolumic relaxation '', 2 ) Inflow, 3 ) `` Isovolumic contraction '', 4 ) `` Ejection ''. ( See Wiggers diagram, which, label-wise, presents the stages as 3, 4, 1, 2, left - to - right. ) Stages 1 ( Isovolumic relaxation ) and 2 ( Inflow : `` Rapid inflow '', `` Diastasis '', and `` Atrial systole '' ) together complete the ventricular `` Diastole '' period, during which blood returning to the heart flows through the atria into the ventricles. Near the end of the `` Diastole '', both atria pump blood into the ventricles during atrial systole, aka atrial kick. Stages 3 and 4 are the ventricular `` Systole '' period, which is the simultaneous pumping of separate blood supplies from the two ventricles -- one to the pulmonary artery and one to the aorta. The time-wise increases / decreases of the heart 's blood volume ( see Wiggers diagram ), are instructive to follow. The red - line tracing of `` Ventricular volume '' provides an excellent track of the two periods and four stages of one cardiac cycle. Start with the Systole ( see the vertical bar marked `` A - V valve closes '' ) at the short - time plateau of Isovolumic contraction stage, then to the rapid loss of blood volume ( or the vertical drop of the red - line tracing ) during the Ejection stage. Now the Diastole period : the low plateau of Isovolumic relaxation stage, followed by the rapid rise, then two slower rises, of the Inflow stage, returning to the plateau of Isovolumic contraction stage. Stages Diastole ( at right ) normally refers to atria and ventricles at relaxation and expansion together -- while refilling with blood returning to the heart. Systole ( left ) typically refers to ventricular systole, during which the ventricles are pumping ( or ejecting ) blood out of the heart through the aorta and the pulmonary veins. Valve configurations during main stages of the cardiac cycle Stage AV valves * Semilunar valves Status of ventricles and atria ; and blood flow 1 Isovolumic relaxation closed closed semilunar ( pulmonary and aortic ) valves close at end of ejection stage ; blood flow stops. 2a Inflow : ( Ventricular filling ) open closed ventricles and atria together relax and expand ; blood flows to the heart during ventricular and atrial diastole. 2b Inflow : ( Ventricular filling with Atrial systole ) open closed ventricles relaxed and expanded ; atrial contraction ( systole ) forces blood under pressure into ventricles during ventricular diastole -- late. 3 Isovolumic contraction closed closed AV valves close at end of ventricular diastole ; blood flow stops ; ventricles begin to contract. 4 Ejection : Ventricular ejection closed open ventricles contract ( ventricular systole ) ; blood flows from the heart -- to the lungs and to rest of body during venticular ejection. Notes : Stages 1, 2a, and 2b together comprise the `` Diastole '' period ; stages 3 and 4 together comprise the `` Systole '' period. based on Ganong Rapid - filling inflow produced by atrial systole during `` ventricular diastole -- late '' Atrioventricular ( AV ) valves = tricuspid valve ; mitral valve Semilunar valves = pulmonary valve ; aortic valve Physiology CG Animated Human Heart cut section showing the atria, ventricles and valves, synced with wiggers diagram The heart is a four - chambered organ consisting of right and left halves. The upper two chambers, the left and right atria, are entry - points into the heart, while the lower two chambers, the left and right ventricles, are responsible for contractions that send the blood through the circulation. The circulation is split into the pulmonary and systemic circulation. The role of the right ventricle is to pump deoxygenated blood to the lungs through the pulmonary trunk and pulmonary arteries. The role of the left ventricle is to pump newly oxygenated blood to the body through the aorta. Rhythmical conduction Heart conducting system Main article : Electrical conduction system of the heart Cardiac muscle has automaticity, which means that it is self - excitable. The muscle contractions are generated by the muscle cell itself or are passed down by another set of specialized cardiomyocytes ( cardiac muscle cells ), called the ' junctional fibers '. This is in contrast with skeletal muscle, which requires nervous stimuli ( either conscious or reflex ) for excitation. The heart 's rhythmic contractions occur spontaneously, although the rate of contraction can be changed by nervous or hormonal influences. For example, stimulating the sympathetic nerve accelerates heart rate while stimulating the vagus nerve decelerates the heart rate. The rhythmic sequence of contractions ( sinus rhythm ), is coordinated by the sinoatrial ( SA ) and atrioventricular ( AV ) nodes. The sinoatrial node, often known as the cardiac pacemaker, is located in the upper wall of the right atrium and is responsible for the wave of electrical stimulation that initiates atrial contraction by creating an action potential. Once the wave reaches the AV node, situated in the lower right atrium, it is delayed there before being conducted through the bundles of His and back up the Purkinje fibers, leading to a contraction of the ventricles. The delay at the AV node allows enough time for all of the blood in the atria to fill their respective ventricles. In the event of severe pathology, the AV node can also act as a pacemaker ; this is usually not the case because its rate of spontaneous firing is considerably lower than that of the SA node and hence it is overridden. Atrial systole Atrial systole is the contraction of the atrial syncytium of cardiac muscle cells of the left and right atria, following electrical stimulation. This conduction takes place via the gap junctions of the connecting intercalated discs. Normally, both atria contract at the same time. The term systole is synonymous with contraction ( movement or shortening ) of a muscle. Electrical systole is the electrical activity that stimulates the cardiac muscle of the heart chambers to make them contract. This is soon followed by mechanical systole, which is the mechanical contraction of the heart. As the atria contract, the blood pressure in each atrium increases, forcing additional blood into the ventricles. The additional flow of blood is called atrial kick. 80 % of the blood flows passively down to the ventricles, so the atria do not have to contract a great amount. Atrial kick is absent if there is loss of normal electrical conduction in the heart, such as during atrial fibrillation, atrial flutter, and complete heart block. Atrial kick is also different in character depending on the condition of the heart, such as stiff heart, which is found in patients with diastolic dysfunction. Atrial systole, also known as auricular systole due to the contraction of the two auricles of the heart, takes approximately 0.1 seconds. Detection Electrical systole of the atria begins with the onset of the P wave on the ECG. The wave of depolarization that stimulates both atria to contract at the same time is due to the sinoatrial node which is located on the upper wall of the right atrium. The sinoatrial node can be detected by catheterization. Ventricular systole Ventricular systole Ventricular systole is the contraction of the ventricular syncytium of cardiac muscle cells of the left and right ventricles, following electrical stimulation. This conduction takes place via the gap junctions of the connecting intercalated discs. At the later part of the ejection phase, although the ventricular pressure falls below the aortic pressure, the aortic valve remains open because of the inertial energy of the ejected blood. The graph of aortic pressure throughout the cardiac cycle displays a small dip ( the `` incisure '' or `` dicrotic notch '' ) which coincides with the aortic valve closure. The dip in the graph is immediately followed by a brief rise ( the `` dicrotic wave '' ) then gradual decline. Just as the ventricles enter into diastole, the brief reversal of flow from the aorta back toward the left ventricle causes the aortic valves to shut. This results in the slight increase in aortic pressure caused by the elastic recoil of the semilunar valves and aorta. The total volume of blood remaining in the ventricle just at the end of the ventricular contraction is called end - systolic volume ( ESV ). Assuming a pulse of 72 beats per minutes, ventricular systole takes 0.3 seconds to complete. Detection Heart sounds Main article : Heart sounds The closing of the mitral and tricuspid valves ( known together as the atrioventricular valves ) at the beginning of ventricular systole cause the first part ( the lubb ) of the `` lubb - dubb '' sound made by the heart as it beats. Formally, this sound is known as the first heart sound, or S. This first heart sound is created by the closure of the mitral and tricuspid valves and is actually a two component sound, M1, T1. The second part ( the dubb ) of the `` lubb - dubb '' ( the second heart sound, or S ), is caused by the closure of the aortic and pulmonary valves at the end of ventricular systole. As the left ventricle empties, its pressure falls below the pressure in the aorta, and the aortic valve closes. Similarly, as the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonary valve closes. The second heart sound is also two components, A2 and P2. The aortic valve closes earlier than the pulmonary valve and they are audibly separated from each other in the second heart sound. This `` splitting '' of S2 is only audible during inhalation. However, some cardiac conduction abnormalities such as left bundle branch block ( LBBB ) allow the P2 sound to be heard before the A2 sound during expiration. With LBBB, inhalation brings A2 and P2 closer together where they can not be audibly distinguished. Electrocardiogram The parts of a QRS complex. Ventricular systole begins at the QRS, Atrial systole begins at P In an electrocardiogram, electrical systole of the ventricles begins at the beginning of the QRS complex. Diastole Cardiac diastole Cardiac diastole is the period of time when the heart relaxes after contraction in preparation for refilling with circulating blood. Ventricular diastole is when the ventricles are relaxing, while atrial diastole is when the atria are relaxing. Together they are known as complete cardiac diastole. During ventricular diastole, the pressure in the ( left and right ) ventricles drops from the peak that it reaches in systole. When the pressure in the left ventricle drops to below the pressure in the left atrium, the mitral valve opens, and the left ventricle fills with blood that was accumulating in the left atrium. The isovolumic relaxation time ( IVRT ) is the interval from the aortic component of the second heart sound, that is, closure of the aortic valve, to onset of filling by opening of the mitral valve. Likewise, when the pressure in the right ventricle drops below that in the right atrium, the tricuspid valve opens, and the right ventricle fills with blood that was accumulating in the right atrium. During diastole the pressure within the left ventricle is lower than that in aorta, allowing blood to circulate in the heart itself via the coronary arteries. See also Apex beat Blood pressure Cardiac action potential Cardiac output Electrocardiogram References Jump up ^ Gersh, Bernard J ( 2000 ). Mayo Clinic Heart Book. New York : William Morrow. pp. 6 -- 8. ISBN 0 - 688 - 17642 - 9. Jump up ^ Topol, Eric J ( 2000 ). Cleveland Clinic Heart Book. New York : Hyperion. pp. 4, 5. ISBN 0 - 7868 - 6495 - 8. Jump up ^ Betts, J. Gordon ( 2013 ). Anatomy & physiology. pp. 787 -- 846. ISBN 1 - 938168 - 13 - 5. Retrieved 11 August 2014. Jump up ^ Topol, Eric J ( 2000 ). Cleveland Clinic Heart Book. New York : Hyperion. pp. 8 -- 10. ISBN 0 - 7868 - 6495 - 8. Jump up ^ Topol, Eric J ( 2000 ). Cleveland Clinic Heart Book. New York : Hyperion. pp. 8 -- 10. ISBN 0 - 7868 - 6495 - 8. Jump up ^ Guyton & Hall 2011, pp. 105 -- 07. Jump up ^ Walter F. Boron, Emile L. Boulpaep ( 2016 ) Medical Physiology ( 3rd Edition ) Elsevier ISBN 978 - 1 - 4557 - 4377 - 3 Jump up ^ Barrett et al. `` '' Ganong 's Review of Medical Physiology 24e `` '' ( 2012 ) Table 30 - 3 Jump up ^ Advanced Biology for You -- Gareth Williams Jump up ^ `` Heart cycle time interval ''. Retrieved 9 September 2013. Jump up ^ Cardiovascular Physiology Concepts by Richard E. Klabunde, Ph. D. : Cardiac Cycle -- Reduced Ejection ( Phase 4 ) Jump up ^ `` VS time interval ''. Retrieved 9 September 2013. Jump up ^ Inductance cardiography ( thoracocardiography ) : A novel, noninvasive technique for monitoring left ventricular filling. Journal of Critical Care, Volume 14, Issue 4, pp. 177 -- 85 External links Interactive cardiac cycle. Interactivephysiology.com Cardiac cycle. University of Utah School of Medicine Heart sounds. UCLA School of Medicine Physiology of the cardiovascular system Heart Cardiac output Cardiac cycle Cardiac output Heart rate Stroke volume Stroke volume End - diastolic volume End - systolic volume Afterload Preload Frank -- Starling law Cardiac function curve Venous return curve Wiggers diagram Pressure volume diagram Ultrasound Fractional shortening = ( End - diastolic dimension End - systolic dimension ) / End - diastolic dimension Aortic valve area calculation Ejection fraction Cardiac index Heart rate Cardiac pacemaker Chronotropic ( Heart rate ) Dromotropic ( Conduction velocity ) Inotropic ( Contractility ) Bathmotropic ( Excitability ) Lusitropic ( Relaxation ) Conduction Conduction system Cardiac electrophysiology Action potential cardiac atrial ventricular Effective refractory period Pacemaker potential Electrocardiography P wave PR interval QRS complex QT interval ST segment T wave U wave Hexaxial reference system Chamber pressure Central venous Right atrial ventricular pulmonary artery wedge Left atrial ventricular Aortic Other Ventricular remodeling Vascular system / Hemodynamics Blood flow Compliance Vascular resistance Pulse Perfusion Blood pressure Pulse pressure Systolic Diastolic Mean arterial pressure Jugular venous pressure Portal venous pressure Regulation of BP Baroreflex Kinin -- kallikrein system Renin -- angiotensin system Vasoconstrictors Vasodilators Autoregulation Myogenic mechanism Tubuloglomerular feedback Cerebral autoregulation Paraganglia Aortic body Carotid body Glomus cell Retrieved from `` https://en.wikipedia.org/w/index.php?title=Cardiac_cycle&oldid=826676697 '' Categories : Cardiovascular physiology Hidden categories : Articles needing additional references from August 2012 All articles needing additional references Talk Contents About Wikipedia Bosanski Català Čeština Dansk Español Euskara فارسی 한국어 Italiano ಕನ್ನಡ Kiswahili Magyar Македонски नेपाली Polski Português Русский Српски / srpski ไทย Українська 粵語 Edit links This page was last edited on 20 February 2018, at 12 : 37. 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Question: the cardiac event that completes ventricular filling is referred to as
Answer: "Diastole"