1. right atrium receives blood LOW in oxygen, or deoxygenated, from all tissues through the superior and inferior vena cavae

2. blood is then enters the right ventricle and is pumped to the lungs through the pulomary artery

3. blood returns from the lungs HIGH in oxygen, or oxygenated, and enters the left atrium through the pulomary veins

4. blood enters the left ventricle and is forcefully pumped into the aorta to be distributed to all organs

Endocardium - thin membrane that lines the chambers and valves

Myocardium - thick muscle layer that makes up most of the heart wall

Epicardium - thin membrane that covers the heart

Pericardium - fibrous sac around the heart

Artium - Upper receiving heart chambers

Ventricle - Lower pumpimg heart chambers

Aorta - largest artery; receives blood from left ventricle and branches to all parts of the body

Sinoatrial (SA) Node: Pacemaker; sets rate of the heartbeat

Atrioventricular (AV) Node: carry stimulation throughout both atria

AV Bundle (Bundle of His): transmits impulses from the AV node to the top of the interventricular septum

Purkinje Fibres: carry stimulation thoughout the walls of the ventricles

- Arteries: Carry blood AWAY from the heart

- All arteries EXCEPT pulmonary (lung) artery and the umbilical artery in the fetus, carry OXYGENATED blood

- Vein: Carries blood BACK to the heart

- All veins EXCEPT the pulmonary (lung) veins, and the umbilical vein in the fetus, carry DEOXYGENATED blood