The cardiac cycle comprises a complete relaxation and contraction of both the atria and ventricles, and lasts approximately 0.8 seconds. Beginning with all chambers in diastole, blood flows passively from the veins into the atria and past the atrioventricular valves into the ventricles. The atria begin to contract (atrial systole), following depolarization of the atria, and pump blood into the ventricles. The ventricles begin to contract (ventricular systole), raising pressure within the ventricles. When ventricular pressure rises above the pressure in the atria, blood flows toward the atria, producing the first heart sound, S1 or lub. As pressure in the ventricles rises above two major arteries, blood pushes open the two semilunar valves and moves into the pulmonary trunk and aorta in the ventricular ejection phase. Following ventricular repolarization, the ventricles begin to relax (ventricular diastole), and pressure within the ventricles drops. As ventricular pressure drops, there is a tendency for blood to flow back into the atria from the major arteries, producing the dicrotic notch in the ECG and closing the two semilunar valves. The second heart sound, S2 or dub, occurs when the semilunar valves close. When the pressure falls below that of the atria, blood moves from the atria into the ventricles, opening the atrioventricular valves and marking one complete heart cycle. The valves prevent backflow of blood. Failure of the valves to operate properly produces turbulent blood flow within the heart; the resulting heart murmur can often be heard with a stethoscope.
cardiac cycle
period of time between the onset of atrial contraction (atrial systole) and ventricular relaxation (ventricular diastole)
diastole
period of time when the heart muscle is relaxed and the chambers fill with blood
end diastolic volume (EDV)
(also, preload) the amount of blood in the ventricles at the end of atrial systole just prior to ventricular contraction
end systolic volume (ESV)
amount of blood remaining in each ventricle following systole
heart sounds
sounds heard via auscultation with a stethoscope of the closing of the atrioventricular valves (“lub”) and semilunar valves (“dub”)
isovolumic contraction
(also, isovolumetric contraction) initial phase of ventricular contraction in which tension and pressure in the ventricle increase, but no blood is pumped or ejected from the heart
isovolumic ventricular relaxation phase
initial phase of the ventricular diastole when pressure in the ventricles drops below pressure in the two major arteries, the pulmonary trunk, and the aorta, and blood attempts to flow back into the ventricles, producing the dicrotic notch of the ECG and closing the two semilunar valves
murmur
unusual heart sound detected by auscultation; typically related to septal or valve defects
preload
(also, end diastolic volume) amount of blood in the ventricles at the end of atrial systole just prior to ventricular contraction
systole
period of time when the heart muscle is contracting
ventricular ejection phase
second phase of ventricular systole during which blood is pumped from the ventricle
1. The cardiac cycle consists of a distinct relaxation and contraction phase. Which term is typically used to refer ventricular contraction while no blood is being ejected?
A) systole
B) diastole
C) quiescent
D) isovolumic contraction
D
2. Most blood enters the ventricle during ________.
A) atrial systole
B) atrial diastole
C) ventricular systole
D) isovolumic contraction
B
3. The first heart sound represents which portion of the cardiac cycle?
A) atrial systole
B) ventricular systole
C) closing of the atrioventricular valves
D) closing of the semilunar valves
C
4. Ventricular relaxation immediately follows ________.
A) atrial depolarization
B) ventricular repolarization
C) ventricular depolarization
D) atrial repolarization
B
1. Describe one cardiac cycle, beginning with both atria and ventricles relaxed.
The cardiac cycle comprises a complete relaxation and contraction of both the atria and ventricles, and lasts approximately 0.8 seconds. Beginning with all chambers in diastole, blood flows passively from the veins into the atria and past the atrioventricular valves into the ventricles. The atria begin to contract following depolarization of the atria and pump blood into the ventricles. The ventricles begin to contract, raising pressure within the ventricles. When ventricular pressure rises above the pressure in the two major arteries, blood pushes open the two semilunar valves and moves into the pulmonary trunk and aorta in the ventricular ejection phase. Following ventricular repolarization, the ventricles begin to relax, and pressure within the ventricles drops. When the pressure falls below that of the atria, blood moves from the atria into the ventricles, opening the atrioventricular valves and marking one complete heart cycle.