Some things you need to memorize about the heart and cardiac cycle:



When the ventricles contract


When the ventricles are relaxed


Happening during systole


Happening during diastole

Semilunar valves

The aortic and pulmonary valves

AV valves

The mitral and tricuspid valves

Calcium channels

Let Ca2+ enter cardiac and smooth muscle cells, where it is used for muscle contraction

Funny channels

Na+ channels in the pacemaker cells, which let Na+ leak in until the cell reaches threshold and fires


The period following depolarization of an individual cardiac muscle cell, when it remains positive because Ca2+ is still entering the cell. During this period the cell is contracting

Sinoatrial node

The cardiac muscle cells that have the largest Ca2+ leak and depolarize most rapidly � the pacemaker

Atrioventricular node

The cells that can pass the depolarization impulse from the atria to the ventricles

Bundle of His or Atrioventricular bundle

The fibers that carry the depolarization impulse from atria to ventricles

P wave

Represents atrial depolarization. Is followed by atrial contraction.

PR interval

Represents the length of time needed for the impulse to go through the AV node and bundle of His

QRS complex

Represents ventricular depolarization. Is followed by ventricular contraction.

T wave

Represents ventricular repolarization. Is followed by ventricular relaxation.

First heart sound (lub)

Caused by the AV valves closing when the ventricles begin to contract, forcing blood up against them

Second heart sound (dub)

Caused by the semilunar valves closing, when the ventricles relax

Pulmonary circuit

The path of blood from RV to lungs to LA

Systemic circuit

The path of blood from LV to body to RA

Heart rate (HR)

Number of heart beats per minute

Stroke volume (SV)

mL of blood moved per heart beat

Cardiac output (CO)

mL of blood moved per minute; HR x SV

Peripheral resistance or Systemic Vascular Resistance or Total Vascular Resistance

The resistance to blood flow caused by capillaries, constricted arterioles or blocked blood vessels. More resistance increases BP.

Blood pressure

The amount of pressure the blood exerts against the walls of the arteries. CO x PR

Pulse pressure

The difference between systolic and diastolic blood pressure