Dissect, display and identify a sheep's heart

Materials needed:

• Dissecting board
• Scalpel
• Dissecting scissors
• Forceps
• Seeker
• Dissecting pins
• Gloves
• Disinfectant
• Sketching paper and pencil
• Sheep heart

Method:

1. Place the heart on the dissecting board with the front (ventral) side facing up. To identify the front side:

• Feel the sidewalls; the left side will feel much firmer than the right side.
• Find a groove extending from the right side of the heart downward.

2. Locate the four chambers of the heart and the main blood vessels.
3. Draw a labelled sketch of the external structure of the heart.
4. Make a shallow cut in the left ventricle and left atrium.
5. Open the heart at the cut to examine the internal structure.
6. Observe and record the different sizes of the chambers.
7. Locate the bicuspid valve between the left atrium and left ventricle (look for two flaps).
8. Insert your finger under the chordae tendinae and notice they extend from the valve to the papillary muscles.
9. Make a shallow cut on the right side of the heart (see diagram).
10. Locate the tricuspid valve between the right atrium and right ventricle (look for three flaps).
11. Find the septum, a thick muscular wall separating the right and left ventricles.
12. Use a scalpel to cut open the aorta and observe the semi-lunar valve (look for three half-moon-shaped flaps).
13. Find two small openings at the base of the aorta just above the semi-lunar valve, leading into the coronary arteries. Insert a seeker into a coronary artery to trace its pathway.
14. Draw a labelled diagram of the internal structure of the heart.
15. Wash and sterilise the dissecting instruments after use.