Final answer:
The middle mediastinum contains the heart, along with other structures such as the superior and inferior vena cavae, the aorta, and the pulmonary trunk.
Step-by-step explanation:
The middle mediastinum is a region within the thoracic cavity, located between the superior mediastinum and the posterior mediastinum. It contains the heart, which is situated medially between the lungs. The heart is surrounded by a tough membrane called the pericardium and resides in its own space called the pericardial cavity. Additionally, the middle mediastinum also houses other structures such as the superior and inferior vena cavae, the aorta, and the pulmonary trunk.