Step 11: The Heart

1. Superior vena cava
2. Right atrium
3. Right ventricle
4. Left ventricle
5. Inferior vena cava
6. Aorta
7. Pulmonary vein
8. Left atrium
9. Pulmonary artery
10. Aortic arch
11. Left superior vena cava

For the most part, there will be no need to separate the heart from the lungs, but you may need to examine the heart. If the heart is touching or is almost touching the diaphragm at the time  the sternum is removed, it is a sign that the heart is enlarged. As the diaphragm is punctured, the pressure in the thoracic cavity will change, causing the heart to retract, so it is a good time to make this observation. As in humans who don't get a great deal of exercise, are obese, or are getting old, the heart of an old, obese, or sedentary mouse will be enlarged. Heart enlargement and heart lesions are typical in older animals. Also, don't be alarmed if the heart is still beating. Because of electric currents running through the body after death, some movement of the heart and various other muscles will continue to occur after euthanasia.

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