Which of the following organs contains a cardiac notch?

The left lung contains the cardiac notch, which is an indentation that accommodates the heart's position in the thoracic cavity. This anatomical feature allows for the heart, which is slightly off-center to the left side of the body, to fit within the confines of the rib cage without impinging upon lung function. The presence of the cardiac notch on the left lung serves as an example of how organs are designed to anatomically coordinate with one another to optimize space and function within the thoracic cavity.

In contrast, the right lung does not have a cardiac notch because it is not necessary for the heart's placement, as the right lung is shorter and broader. The trachea is a tube that directs air to the lungs and does not contain notches or indentations associated with other organs. The heart itself, while central to circulation, does not have a notch, as it is a muscular organ rather than one that would have such anatomical features. Thus, the correct answer is clear, as the left lung uniquely provides the cardiac notch that facilitates the positioning of the heart.