What anatomical landmark lies just below the superior border of the heart?

The correct choice is the second rib as it serves as an important anatomical reference point for locating the heart. The superior border of the heart typically aligns with the level of the second rib, particularly at the sternal angle (also known as the angle of Louis), which is located at the level of the second rib. This anatomical correlation aids in various medical assessments, including auscultation, palpation, and surgical interventions.

Understanding this relationship helps medical professionals accurately identify the location of the heart, which is critical for procedures like placing central lines or conducting physical examinations. The focus on the second rib emphasizes its role in demarcating the top of the heart's border and facilitating further anatomical or clinical engagements related to cardiovascular health.