The heart is located in the mediastinum. It is enclosed by a double-walled sac called the pericardium. Its base points upward and its apex tips downward, facing the diaphragm.
The anterior surface of the external sheep heart has a curved anterior_interventricular_sulcus that runs across its surface and disappears under the left auricle, then reappears on the posterior side.
The posterior surface of the sheep heart includes the posterior_interventricular_sulcus that runs vertically across its surface.
Both the anterior and posterior sulci contain coronary_vessels. The two auricles expand to accommodate blood volume for the two upper chambers of the heart, which are called the atria (sing: atrium).
Three vessels cross the base of the heart on the anterior side. From left to right they are: the pulmonary_trunk, aorta, and brachiocephalic_artery. On the posterior side of the heart, from left to right, are the pulmonary_veins and the vena_cava_veins.