Week 2: Cardiac Cycle

15 vocabulary flashcards covering key terms related to the cardiac conduction system, ECG components, and cardiac cycle physiology.

Sinoatrial (SA) Node

Patch of pacemaker cells in the right atrium that initiates each heartbeat and sets the heart rate; the heart’s primary pacemaker.

Atrioventricular (AV) Node

Node located near the interatrial septum that delays impulses and serves as the electrical gateway to the ventricles; can pace the heart at 40–50 bpm if the SA node fails.

Purkinje Fibers

Fast-conducting fibers in the ventricular myocardium that distribute electrical impulses, triggering synchronized ventricular contraction.

Cardiac Output (CO)

The volume of blood ejected by each ventricle in one minute; calculated as heart rate multiplied by stroke volume (CO = HR × SV).

Stroke Volume (SV)

Amount of blood pumped out of a ventricle with each heartbeat; about 70 mL at rest.

End-Diastolic Volume (EDV)

Maximum volume of blood in a ventricle at the end of filling (diastole); roughly 130 mL.

End-Systolic Volume (ESV)

Volume of blood remaining in a ventricle after contraction (systole); typically about 60 mL.

Sinus Rhythm

Normal heartbeat regulated by the SA node, usually 60–100 beats per minute (average 70–80 bpm).

Ectopic Focus

An abnormal pacemaking site that assumes control when the SA node is impaired; common example is the AV node.

QRS Complex

Tall, rapid ECG deflection representing ventricular depolarization.

T Wave

ECG deflection that signifies ventricular repolarization (recovery).

P Wave

First small ECG deflection indicating atrial depolarization.

Ventricular Fibrillation (VFib)

Life-threatening arrhythmia with chaotic, irregular ECG waves that prevent effective ventricular pumping.

Frank-Starling Law of the Heart

Concept that the force of ventricular contraction is proportional to end-diastolic volume; the heart pumps out what it receives.

Afterload

The resistance the ventricles must overcome to eject blood; elevated by conditions like hypertension, reducing stroke volume.