Final answer:
The apex of the heart is the most inferior region that rests on the diaphragm, positioned to the left of the sternum and often associated with the cardiac notch of the left lung.
Step-by-step explanation:
The apex of the heart is the most inferior region that rests on the diaphragm. This tip of the heart reaches just to the left of the sternum, nestled between the junctions of the fourth and fifth ribs close to their costal cartilages. The apex's slight tilt towards the left is observable as a depression in the medial surface of the left lung's inferior lobe, otherwise known as the cardiac notch. The diaphragm, which the heart apex contacts, is a dome-shaped muscular structure assisting in respiration, demarcating the thoracic cavity from the abdominal cavity and featuring openings for structures like the inferior vena cava and the esophagus to pass through.