Final answer:
The inferior border of the heart, mainly the right ventricle, is known as the a). apex. It is located at the tip of the left ventricle, just to the left of the sternum between the fourth and fifth ribs.
Step-by-step explanation:
The inferior border of the heart, mainly of the right ventricle, is known as the apex. The apex is the tip of the left ventricle and it is the part of the heart that lies just to the left of the sternum between the junction of the fourth and fifth ribs, close to the costal cartilages. The base of the heart is the superior surface where the great vessels connect, but it is not the inferior border.
The septum refers to the walls dividing the heart into chambers and is not a border. The atrium is part of the upper chamber of the heart, thus it is not considered the inferior border of the heart.
The right ventricle, which makes up a significant portion of the heart's anterior surface, works alongside the left ventricle in pumping blood but to different circuits; the right ventricle to the pulmonary and the left ventricle to the systemic circuit. Understanding the anatomy and orientation of these cardiac structures is essential for clinical practices such as auscultation and interpretation of medical images.