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The Cardiac Cycle
Chapter 3
Ara G. Tilkian, MD, FACC
Patricia L. Thomas, MBA, RCIS
The Cardiac Cycle
Atrial and Ventricular Diastole and Systole
The sounds of the Heart
The valves and papillary Muscles
Valvular Pathophysiology
Atrial & Ventricular Diastole
• Phase of Cardiac Cycle (see 3.1 A)
• Atrial Diastole
– Venous blood enters RA via SVC & IVC
– Pulmonary Blood enters the LA via the 4 PV
Atrial and Ventricular Diastole
Atrial & Ventricular Diastole
• Ventricle Diastole-two phases
– #1 Early passive filling (both atria/ventricles
– #2 Late active filling (atrial systole or AKick)(see 3.1 B)
– 3rd and 4th heart sounds (S3 & S4)
– 3rd HS the initial rapid filling phase early in
– 4th HS the final filling phase at the end of
Atrial Systole, Late Active Filling Phase
Atrial and Ventricular Systole
• Atrial Systole
– Occurs in response to depolarization
– Contraction occurs toward the end of
ventricular diastole (atrial-kick) before the
ventricles contract
– Electrical impulse traveling to the ventricles is
normally delayed momentarily in the AV node
premitting the atrial contraction to augment
ventricular filling.
Atrial and Ventricular Systole
• Ventricular Systole
– Occurs in response to the depolarization wave within
the ventricles the QRS wave
– Venous blood is propelled from the RV the the PA for
– Oxygenated blood is propelled from the LV through
the AO to systemic circulation
– Onset of ventricular systole the AV and PV are still
closed. (isovolumic ventricular contraction) (see 3-1
– When the aortic and pulmonic valves open (rapid
Isovolumic Ventricular Contraction,
Beginning of Ventricular Systole
Ventricular Systolic Ejection
The Sound of the Heart
• S1 closure of the Mitral & Tricuspid valves
• S2 closure of the Aortic & Pulmonic
• S3 passive ventricular filling sound
(early diastole)
• S4 active ventricular filling sound
(late diastole)
The First Heart /Ejection Sounds
• Mitral valve closure closely followed by tricuspid
valve closure
• Closure occurs when the onset of ventricular
systole abruptly raises the ventricular pressure
above that of the atria
• The aortic valve opens (AO) followed by the
opening of the pulmonic valve (PO)
• The opening of the two semilunar valves is
normally not heart
• A diseased aortic/pulmonic valve may produce an
ejection sound
The Second Heart Sound
• Aortic valve closure (AC) closely followed by
pulmonic valve closure (PC)
• The two valves close when the systolic ejection into the
aorta/pulmonary artery declines and rising pressure in
these great vessels exceeds the pressures in the
respective ventricles, reversing the flow and causing
the closure of their valves.
• Isovolumic relaxation is after the closure of the AV/PV
but before opening of the MV/TV results in a rapid fall
in ventricular pressure
• Ventricular = Atrial pressure MV/TV opens silently
• If valves are abnormal/stenosed an opening snap (OS)
or click may be heard
The Third Heart Sound
• Rapid filling of the left ventricle
following the opening of the mitral
• Physiological in young people
• Pathological in people with
congestive heart failure or ventricular
The Fourth Heart Sound
• Blood being forced into a stiff or
noncompliant LV by the atrial contraction
• Late diastolic event that should be silent
• Atrial diastolic gallop when heard
• Stiff ventricles may be caused by
hypertension, ischemia, outlet obstruction,
or hypertrophic or infiltrative myopathies
The Valves and Papillary Muscles
The Atrioventricular Valves
• Competence of the AV valves depends on
the chordae tendineae (CT)
• CT are attached to the free edges and
ventricular surfaces of the valve cusps
• CT are attached to fingerlike projections of
muscle tissue from the endocardium called
the papillary muscles
The Semilunar Valves
• Aortic and Pulmonic valves are
called semilunar because of their
half-moon shape, a structure that
prevents the backflow of blood form
the aorta and pulmonary artery into
the ventricles.
Valvular Pathophysiology
• Mitral/Tricuspid stenosis-when these values
are unable to open completely or have a
congenitally small opening there is an
obstruction to the free flow of blood
• Competent- a properly functioning valve
• Regurgitant/Insufficient-leaky or stenosed
Tilkian, Ara MD Understanding Heart Sounds and Murmurs,
Fourth Edition, W.B. Sunders Company. 2002, pp. 26-33.

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