a small fluid filled space surrounding the heart.

• A. Pleural cavity
• B. Mediastinum cavity
• C. Pericardial cavity
• D. Abdominal cavity

Answer: (C)

The key idea is the pericardial cavity, a small fluid-filled space between the two layers of serous pericardium around the heart. This cavity contains pericardial fluid that lubricant-wise reduces friction as the heart beats, allowing smooth movement within the sac.

The heart sits inside a fibrous pericardium, and the serous layer forms two layers: the parietal layer lining the fibrous sac and the visceral layer covering the heart itself. The gap between these serous layers is the pericardial cavity. While this space lies within the mediastinum, it is the specific fluid-filled area surrounding the heart.

In contrast, the pleural cavities surround the lungs, the mediastinum is the central thoracic compartment that houses the heart and other structures (not a fluid-filled space around the heart by itself), and the abdominal cavity contains digestive and other organs below the diaphragm.