Across
- 3. Inner lining of the heart
- 7. Thin-walled vessel that carries blood from tissues back to the heart
- 8. Muscular middle layer of the heart
- 10. Double-layered membrane surrounding the heart
- 11. Smallest type of blood vessel
- 13. Structure in veins or the heart that closes and opening
- 14. Relaxation phase of the heartbeat
- 15. Small vein
Down
- 1. Gas that enters the blood through the lungs
- 2. Beat of the heart felt through the walls of the arteries
- 4. The two lower chambers of the heart
- 5. Contraction phase of the heartbeat
- 6. Largest type of blood vessel
- 9. Small artery
- 12. Largest artery in the body