When locating the vessels of the heart, remember that the pulmonary artery is the vessel that is in the front of the heart.  Use colored pencils to tag each vessel and help you keep track of the right and left side of the heart.

Directly behind the pulmonary is a much thicker vessel, the aorta. The aorta sends oxygenated blood from the heart to the entire body. You may be able to find a branch of the aorta, the brachiocephalic artery attached to it. This vessel will deliver blood to the head and front legs of the sheep.

Toward the back of the heart are two veins that return blood to the heart. The vena cava is located on the right side of the heart and returns deoxygenated blood to the right atrium.

The pumonary veins return oxygenated blood from the lungs to the left atrium of the heart. It is the only vein of the body that carries oxyygenated blood.

The pulmonary artery delivers blood from the heart to the lungs where it will return to the heart via the pulmonary vein. This heart to lungs and back to heart is known as pulmonary circulation. Circulation throughout the body and in its return is known as systemic circulation.