Section 19.3: Cardiac Cycle - Terms

Cardiac Cycle

The period of time that begins with contraction of the atria and ends with ventricular relaxation.

Systole

The period of contraction that the heart undergoes while it pumps blood into circulation.

Diastole

The period of relaxation that occurs as the chambers fill with blood.

Pressure Gradient

The movement of fluids from regions of higher pressure to regions of lower pressure.

Atrial Systole

The contraction of the atria following depolarization, represented by the P wave of the ECG, contributing to ventricular filling.

Ventricular Systole

The contraction of the ventricles following depolarization, represented by the QRS complex in the ECG, divided into isovolumic contraction and ventricular ejection phases.

End Diastolic Volume (EDV)

The volume of blood in the ventricles at the end of atrial systole, approximately 130 mL in a resting adult.

Isovolumic Contraction

The initial phase of ventricular systole where the volume of blood remains constant as pressure rises but semilunar valves remain closed.

Ventricular Ejection Phase

The phase of ventricular systole where pressure exceeds that in the pulmonary trunk and aorta, allowing blood to be ejected from the heart.

Stroke Volume

The amount of blood pumped by each ventricle per beat, normally 70–80 mL.

End Systolic Volume (ESV)

The volume of blood remaining in the ventricle after contraction, typically 50–60 mL.

Ventricular Diastole

The relaxation of the ventricles following repolarization, represented by the T wave of the ECG, divided into isovolumic relaxation and late ventricular diastole phases.

Isovolumic Ventricular Relaxation

The early phase of ventricular diastole where the volume of blood remains constant as pressure falls and semilunar valves close.

Heart Sounds

Audible sounds produced by the closing of heart valves, including S1 ('lub') and S2 ('dub').

Murmur

An unusual sound from the heart caused by turbulent blood flow, graded on a scale of 1 to 6.