QuestionSBA
QuestionChoice
Action potentials from the sinoatrial node coordinate synchronous atrial contraction. This increases the pressure in the atria above that in the ventricles, causing the tricuspid and mitral valves to open and the active filling of the ventricles. An **S4** heart sound may be heard here if the atria are contracting against a stiff or hypertrophic ventricle. This is a pathological heart sound.
10024397
c
Atrial contraction
QuestionChoice
Ventricular filling occurs just after ventricular relaxation. Relaxation of the ventricular walls increases the internal volume of the ventricle which decreases the pressure. Due to passive filling and atrial contraction, the pressure in the atria increases and blood flows down the pressure gradient, filling the ventricles with blood. At this stage, the aortic and pulmonary valves are already closed. The **S3** heart sound may be heard here which indicates vigorous refilling of the ventricles. This may be heard in younger individuals and may not be pathological.
10024399
e
Ventricular filling
QuestionChoice
Ventricular ejection refers to the flow of blood from the ventricles into the aorta and pulmonary artery. During this stage, the aortic and pulmonary valves are **open**. No heart sounds are heard during this stage.
10024398
d
Ventricular ejection
QuestionChoice
Once blood has been ejected from the ventricles into the aorta and pulmonary artery, the pressure in these vessels becomes higher than the pressure in the ventricles. This causes the aortic and pulmonary valves to close to prevent backflow of blood into the heart. The S2 heart sound indicates the **closure** of the aortic and pulmonary valves.
10024395
a
Ventricular relaxation
QuestionChoice
During ventricular contraction, there is a higher pressure in the ventricles compared to the atria. To prevent backflow of blood into the atria, the mitral and tricuspid valves close. This is indicated by the **S1** heart sound.
10024396
b
Ventricular contraction
Concept
Chapter
2693
4231
Blood flow through the heart
Topic
159
Cardiovascular physiology
17277
The cardiac cycle describes the flow of blood through the heart.

What best describes the stage in the cardiac cycle that begins with the S2 heart sound?
a