| A | B |
|---|
| heart | muscular organ that pumps blood |
| pacemaker | sends out signals from the right atrium to make the heart muscle contract |
| arteries | carry blood away from the heart. |
| capillaries | are tiny vessels where substance is exchanged between blood and body cells. |
| carry blood back to the heart. | veins |
| Blood leaves the left ventricle through the | aorta |
| is a flap that prevents blood from flowing backwards | valve |
| The upper chamber of the heart is called an | atrium |
| The lower chamber of the heart is called the | ventricle |
| What receives blood into the heart. | Atrias |
| largest artery | aorta |
