Cardiac Notch: Anatomical Location and Clinical Significance

The cardiac notch is a concave impression on the anterior border of the left lung that accommodates the heart's apex.

• Level: 4th–5th intercostal space, just lateral to the midclavicular line.
• Boundaries: Inferiorly by the inferior lobe; superiorly by the lingula (tongue-like projection of the upper lobe).

It allows the left lung to wrap around the heart, optimizing thoracic space. On imaging, the cardiac notch appears as a radiolucent curve along the left heart border. Pathology (e.g., left upper lobe collapse) can obliterate the notch—a useful radiographic sign.