The Steps of The Cardiac Cycle “The Rhythm is gonna get you”

Atrial Systole  Lasts 0.1 sec  Atria contract, and the ventricles relax  SA node depolarizes  This causes a P wave on an EKG  Forces blood through the open AV valves into the ventricles  Creates Systole  Atrial Systole contributes to the final forced push of about 25 mL of blood into the ventricles from the atria

Ventricular Systole  Ventricles depolarize and the atria relax  Lasts seconds  At the beginning of this phase the pressure rises in the ventricle chambers and it pushes blood against the AV valves forcing them shut  Myocardium begins to contract but does not exert force right away  As the ventricles begin to contract, pressure rises since the valves are closed off

Ventricular Systole Cont  Once left ventricular pressure rises above about 80 mmHg and right ventricular pressure rises above 20 mmHg, both semilunar valves open and blood is ejected  Pressure continues to rise in the left ventricle to about 120 mmHg  Rises to about mmHg in the right ventricle  At the end of this phase the T wave of the EKG marks the point of ventricular repolarization  This is the point where they cannot contract

Relaxation Period  Lasts about seconds  Marks the time when the atria and ventricles both relax  SL valves close off since blood begins to flow back due to the lack of pressure from the ventricles  As soon as the ventricular pressure falls below the atrial pressure the AV valves open up and the filling process begins over again  At the end of the relaxation period the ventricles are about ¾ full and the next cycle begins  One cycle lasts 0.8 sec in an average heart

Cardiac Cycle Process Diagrams Step-by-Step Copyright © 2007 by John Wiley & Sons, Inc.

(d) Volume in ventricle (mL) (c) Heart sounds (b) Pressure (mmHg) (a) ECG P R Q S Dicrotic wave Left atrial pressure Aortic pressure Left ventricular pressure T Atrial contraction Atrial contraction Isovolumetric contraction Isovolumetric relaxation Ventricular ejection Ventricular filling (e) Phases of the cardiac cycle 0.3 sec 0.1 sec 0.4 sec Ventricular systole Relaxation period Atrial systole S1S2S3S4 1 Atrial depolarization

(d) Volume in ventricle (mL) (c) Heart sounds (b) Pressure (mmHg) (a) ECG P R Q S Dicrotic wave Left atrial pressure Aortic pressure Left ventricular pressure T Atrial contraction Atrial contraction Isovolumetric contraction Isovolumetric relaxation Ventricular ejection Ventricular filling (e) Phases of the cardiac cycle 0.3 sec 0.1 sec 0.4 sec Ventricular systole Relaxation period Atrial systole S1S2S3S Atrial depolarization Begin atrial systole

(d) Volume in ventricle (mL) (c) Heart sounds (b) Pressure (mmHg) (a) ECG P R Q S Dicrotic wave Left atrial pressure Aortic pressure Left ventricular pressure T Atrial contraction Atrial contraction Isovolumetric contraction Isovolumetric relaxation Ventricular ejection Ventricular filling (e) Phases of the cardiac cycle End (ventricular) diastolic volume 0.3 sec 0.1 sec 0.4 sec Ventricular systole Relaxation period Atrial systole S1S2S3S Atrial depolarization Begin atrial systole End (ventricular) diastolic volume

(d) Volume in ventricle (mL) (c) Heart sounds (b) Pressure (mmHg) (a) ECG P R Q S Dicrotic wave Left atrial pressure Aortic pressure Left ventricular pressure T Atrial contraction Atrial contraction Isovolumetric contraction Isovolumetric relaxation Ventricular ejection Ventricular filling (e) Phases of the cardiac cycle 0.3 sec 0.1 sec 0.4 sec Ventricular systole Relaxation period Atrial systole S1S2S3S Atrial depolarization Begin atrial systole End (ventricular) diastolic volume Ventricular depolarization End (ventricular) diastolic volume

(d) Volume in ventricle (mL) (c) Heart sounds (b) Pressure (mmHg) (a) ECG P R Q S Dicrotic wave Left atrial pressure Aortic pressure Left ventricular pressure T Atrial contraction Atrial contraction Isovolumetric contraction Isovolumetric relaxation Ventricular ejection Ventricular filling (e) Phases of the cardiac cycle 0.3 sec 0.1 sec 0.4 sec Ventricular systole Relaxation period Atrial systole S1S2S3S Atrial depolarization Begin atrial systole End (ventricular) diastolic volume Ventricular depolarization Isovolumetric contraction End (ventricular) diastolic volume

(d) Volume in ventricle (mL) (c) Heart sounds (b) Pressure (mmHg) (a) ECG P R Q S Dicrotic wave Left atrial pressure Aortic pressure Left ventricular pressure T Atrial contraction Atrial contraction Isovolumetric contraction Isovolumetric relaxation Ventricular ejection Ventricular filling (e) Phases of the cardiac cycle 0.3 sec 0.1 sec 0.4 sec Ventricular systole Relaxation period Atrial systole S1S2S3S Atrial depolarization Begin atrial systole End (ventricular) diastolic volume Ventricular depolarization Isovolumetric contraction Begin ventricular ejection End (ventricular) diastolic volume 5

(d) Volume in ventricle (mL) (c) Heart sounds (b) Pressure (mmHg) (a) ECG P R Q S Dicrotic wave Left atrial pressure Aortic pressure Left ventricular pressure T Atrial contraction Atrial contraction Isovolumetric contraction Isovolumetric relaxation Ventricular ejection Ventricular filling (e) Phases of the cardiac cycle Stroke volume 0.3 sec 0.1 sec 0.4 sec Ventricular systole Relaxation period Atrial systole S1S2S3S Atrial depolarization Begin atrial systole End (ventricular) diastolic volume Ventricular depolarization Isovolumetric contraction Begin ventricular ejection End (ventricular) systolic volume End (ventricular) diastolic volume 6 5

(d) Volume in ventricle (mL) (c) Heart sounds (b) Pressure (mmHg) (a) ECG P R Q S Dicrotic wave Left atrial pressure Aortic pressure Left ventricular pressure T Atrial contraction Atrial contraction Isovolumetric contraction Isovolumetric relaxation Ventricular ejection Ventricular filling (e) Phases of the cardiac cycle Stroke volume 0.3 sec 0.1 sec 0.4 sec Ventricular systole Relaxation period Atrial systole S1S2S3S Atrial depolarization Begin atrial systole End (ventricular) diastolic volume Ventricular depolarization Isovolumetric contraction Begin ventricular ejection End (ventricular) systolic volume Begin ventricular repolarization End (ventricular) diastolic volume

(d) Volume in ventricle (mL) (c) Heart sounds (b) Pressure (mmHg) (a) ECG P R Q S Dicrotic wave Left atrial pressure Aortic pressure Left ventricular pressure T Atrial contraction Atrial contraction Isovolumetric contraction Isovolumetric relaxation Ventricular ejection Ventricular filling (e) Phases of the cardiac cycle Stroke volume 0.3 sec 0.1 sec 0.4 sec Ventricular systole Relaxation period Atrial systole S1S2S3S Atrial depolarization Begin atrial systole End (ventricular) diastolic volume Ventricular depolarization Isovolumetric contraction Begin ventricular ejection End (ventricular) systolic volume Begin ventricular repolarization Isovolumetric relaxation End (ventricular) diastolic volume

(d) Volume in ventricle (mL) (c) Heart sounds (b) Pressure (mmHg) (a) ECG P R Q S Dicrotic wave Left atrial pressure Aortic pressure Left ventricular pressure T Atrial contraction Atrial contraction Isovolumetric contraction Isovolumetric relaxation Ventricular ejection Ventricular filling (e) Phases of the cardiac cycle Stroke volume 0.3 sec 0.1 sec 0.4 sec Ventricular systole Relaxation period Atrial systole S1S2S3S Atrial depolarization Begin atrial systole End (ventricular) diastolic volume Ventricular depolarization Isovolumetric contraction Begin ventricular ejection End (ventricular) systolic volume Begin ventricular repolarization Isovolumetric relaxation Ventricular filling End (ventricular) diastolic volume 8 9

(d) Volume in ventricle (mL) (c) Heart sounds (b) Pressure (mmHg) (a) ECG P R Q S Dicrotic wave Left atrial pressure Aortic pressure Left ventricular pressure T Atrial contraction Atrial contraction Isovolumetric contraction Isovolumetric relaxation Ventricular ejection Ventricular filling (e) Phases of the cardiac cycle 0.3 sec 0.1 sec 0.4 sec Ventricular systole Relaxation period Atrial systole S1S2S3S4 1 Atrial depolarization