Mechanical Events of the Cardiac Cycle – Key Vocabulary

Vocabulary flashcards covering the major mechanical and functional terms discussed in the lecture on the cardiac cycle.

Cardiac Cycle

One complete sequence of heart events, including relaxation (diastole) and contraction (systole) of atria and ventricles.

Diastole

Phase of cardiac muscle relaxation when chambers fill with blood.

Systole

Phase of cardiac muscle contraction when chambers eject blood.

Passive Filling

Ventricular filling that occurs while all four chambers are relaxed; requires no cellular energy.

Active Filling

Additional ventricular filling caused by atrial contraction (atrial systole).

Atrial Systole

Contraction of the atria that tops off ventricular volume; part of active filling.

Ventricular Systole

Contraction of the ventricles, divided into isovolumetric contraction and ejection phases.

Isovolumetric Contraction

Early ventricular systole when all valves are closed; pressure rises but volume stays constant.

Ejection Phase

Part of ventricular systole when semilunar valves open and blood is pumped into the arteries.

Isovolumetric Relaxation

Early ventricular diastole when all valves are closed; pressure falls but volume stays constant.

SA (Sinoatrial) Node

Primary pacemaker of the heart that initiates each cardiac cycle.

AV (Atrioventricular) Node

Conductive tissue that delays the impulse between atria and ventricles, allowing sequential contraction.

AV Node Delay

Brief pause in electrical conduction that ensures atrial contraction finishes before ventricular contraction begins.

Fibrous Skeleton of the Heart

Connective tissue framework that electrically insulates atria from ventricles and anchors valves.

Atrioventricular (AV) Valves

Tricuspid and mitral valves; open when atrial pressure exceeds ventricular pressure.

Semilunar Valves

Pulmonary and aortic valves; open when ventricular pressure exceeds arterial pressure.

Pressure Gradient

Difference in pressure that drives blood flow from high to low pressure regions.

Left Ventricular Pressure

Blood pressure within the left ventricle; rises sharply during systole and falls during diastole.

Atrial Pressure

Blood pressure within the atria; slightly increases during atrial systole and passive filling.

Aortic Pressure

Pressure within the aorta; influences opening/closing of the aortic semilunar valve.

Heart Sound S1 ("lubb")

Sound produced at the start of isovolumetric contraction when AV valves close.

Heart Sound S2 ("dubb")

Sound produced at the start of isovolumetric relaxation when semilunar valves close.

Turbulent Blood Flow

Erratic blood movement through a narrow opening under high pressure; source of heart sounds.

Heart Murmur

Abnormal heart sound occurring outside normal S1-S2 timing, usually due to structural defects causing turbulent flow.

Stroke Volume (Residual Mention)

Amount of blood ejected by a ventricle in one beat; some blood always remains after ejection.