Cardiac cycle of the left next of the heart. The electrocardiogram (EKG) listed below the diagram reflects the corresponding waves with each phase of the cardiac cycle. The bottom line represents the first and 2nd heart sounds.

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The cardiac cycle to represent the hemodynamic and electric alters that take place in systole and diastole. It has plenty of phases.

Phases the the Cardiac Cycle

Isovolumetric ventricular convulsion (a-b): This phase marks the start of systole and also starts with the figure of the QRS facility on the EKG and also the closure of the AV valves at point (a). V all valves closed, the ventricle generates hopeful pressure there is no any adjust in its volume (isovolumetric) to overcome the semilunar valves resistance that open at suggest (b). This phase generally lasts for 6% that the cardiac cycle.Rapid ejection (b-c): together the semilunar valves open at suggest (b), over there is a fast ejection that blood as result of increased ventricular contractility. The arterial pressure increases until getting to its best at point (c). This phase typically lasts for 13% of the cardiac cycle.Reduced ejection (c-d): This phase marks the start of ventricular repolarization as depicted by the onset of the T wave on the EKG. Repolarization leader to a rapid decline in ventricular pressures and hence the reduced rate the ejection. However, part forward flow of blood continues second to remnant kinetic power from the ahead phase. This phase generally lasts because that 15% of the cardiac cycle.Isovolumetric be safe (d-e): once the ventricular pressure drop listed below the diastolic aortic and also pulmonary pressures (80 mmHg and 10 mmHg respectively), the aortic and also pulmonary valves close creating the second heart sound (point d). This marks the beginning of diastole. The ventricles generate an unfavorable pressure without changing their volume (isovolumetric) so that the ventricular push becomes reduced than the atrial pressure. This phase usually lasts because that 8% the the cardiac cycle.Ventricular filling (e-a): together the AV valves open at point (e), ventricular filling starts. The initial rapid filling is mostly augmented by ventricular suction which outcomes from ventricular untwisting and the return of each ventricular muscle fiber to its slack length. The ventricular pressure slowly increases until it equates to the atrial pressure and the AV valves near (point a). This phase commonly lasts because that 44% that the cardiac cycle.Atrial contraction: Finally, close to the end of ventricular diastole, the atrial contraction contributes around 10% that the ventricular pour it until it is full volume. This is represented by the P wave on the EKG of the adhering to cycle. This phase typically lasts for 14% that the cardiac cycle.

Heart Sounds

normal pressures in miscellaneous chambers that the heart


The an initial heart sound (S1)represents closure the the atrioventricular (mitral and tricuspid) valves together the ventricular pressures exceed atrial pressure at the start of systole (point a). S1 is generally a solitary sound because mitral and tricuspid valve closure occurs almost simultaneously. Clinically, S1 synchronizes to the pulse.

The 2nd heart sound (S2) to represent closure that the semilunar (aortic and pulmonary) valves (point d). S2 is usually split due to the fact that the aortic valve (A2) closes prior to the pulmonary valve (P2). The closing press (the diastolic arterial pressure) ~ above the left is 80 mmHg as contrasted to only 10 mmHg ~ above the right. This greater closing pressure leads to previously closure of the aortic valve. In addition, the much more muscular and stiff "less compliant" left ventricle (LV) empties previously than the appropriate ventricle. The venous go back to the ideal ventricle (RV) increases during inspiration due to negative intrathoracic pressure and P2 is even more delayed, so it is normal for the separation of the 2nd heart sound to widen during inspiration and also to narrow throughout expiration. Clinically, this is more remarkable with slow heart rates.

The third heart sound (S3)represents a transition from quick to sluggish ventricular pour it until it is full in early diastole. S3 might be heard in typical children.

The 4th heart sound (S4) is an abnormal so late diastolic sound caused by forcible atrial contraction in the existence of lessened ventricular compliance.


Abnormally vast splitting the S2 may occur in:

a) RV volume overload, such as atrial septal defect (ASD) and anomalous pulmonary venous connection. In this cases, the split is usually vast and "fixed" through no difference in between inspiration and expiration because of fixed RV volume (see ASD section)

b) RV outflow obstruction, such as pulmonary stenosis (PS)

c) delay RV depolarization such as finish right bundle branch block


Narrow separating of S2 occurs in:

a) Pulmonary hypertension together the pulmonary valve close the door earlier because of high pulmonary resistance

b) Mild to moderate aortic stenosis together the A2 is delayed


Single S2 may occur:

a) If among the semilunar valves is missing, together in pulmonary or aortic valve atresia and truncus arteriosus

b) If both valves close concurrently as in pulmonary hypertension v equal pulmonary and aortic arterial pressures

c) If both valves close concurrently as in twin outlet single ventricle or in large VSD with equal ventricular pressures

d) Posterior displacement the the pulmonary valve far from the chest wall surface as in d-TGA

Paradoxical dividing of S2 (P2 is heard before A2) wake up in:

a) significant aortic stenosis

b) Left bundle branch block

In both conditions, the aortic valve (A2) close the door after the pulmonary valve (P2). Since the respiration just affects P2, its effect in paradoxical separating is opposing of normal, i.e. Inspiration causes narrow dividing while expiration causes vast splitting of S2.

Heart Murmurs

Murmurs are added sounds generated by rough blood flow in the heart and also blood vessels. Murmurs may be systolic, diastolic or continuous.

Grading that systolic mumers based on thier intensityI/VI: barely audibleII/VI: Faint yet easily audibleIII/VI: according to murmur there is no a palpable thrillIV/VI: loud murmur v a palpable thrillV/VI: really loud murmur heard with stethoscope easy on chestVI/VI: very loud murmur that deserve to be heard there is no a stethoscope

Systolic murmurs room the most common varieties of murmurs in children and also based on their timing in ~ systole, they space classified into:

a) Systolic ejection murmurs (SEM, crescendo-decrescendo) result from turbulent blood flow as result of obstruction (actual or relative) across the semilunar valves, outflow tracts or arteries. The murmur is heard shortly after S1 (pulse). The soot of the murmur increases as an ext blood flows throughout an obstruction and also then decreases (crescendo-decrescendo or diamond shaped). Innocent murmurs space the most common reason of SEM (see below). Other reasons include stenotic lesions (aortic and pulmonary stenosis, coarctation the the aorta, Tetralogy of Fallot (TOF)) or loved one pulmonary stenosis because of increased flow from one ASD

Crescendo decrescendo murmur

b) Holosystolic (regurgitant) murmurs start at the start of S1 (pulse) and also continue come S2. Examples: ventricular septal defect (VSD), mitral and also tricuspid valve regurgitation.

Holosystolic murmur

c) Decrescendo systolic murmur is a subtype that holosystolic murmur that might be heard in patients with little VSDs. In the latter component of systole, the small VSD might close or become so tiny to not allow discernible circulation through and the murmur is no much longer audible.

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Decrescendo murmur

Diastolic murmurs space usually abnormal, and also may be early, mid or late diastolic.