Final answer:
The inferior surface of the pericardial sac, not the heart tissue itself, fuses with the central tendon of the diaphragm, ensuring the heart's correct placement in the thoracic cavity.
Step-by-step explanation:
The question concerns the anatomical relationship between the heart and the diaphragm, specifically asking about which part of the heart fuses with the central tendon of the diaphragm. The inferior surface of the pericardial sac, which wraps around the heart, fuses with the central tendon of the diaphragm. This pericardial sac provides a double-walled protective layer around the heart and allows the heart to beat in a relatively frictionless environment. It does not directly fuse with the heart tissue itself.
The central tendon is an important part of the diaphragm, which is the primary muscle involved in the process of breathing. The muscle fibers of the diaphragm converge on the central tendon, giving it a trefoil shape. The heart sits on top of the diaphragm, and the pericardial sac attaches to the central tendon, ensuring the appropriate positioning of the heart within the thoracic cavity.