Anatomical Position of the Heart Relative to the Lungs
The heart lies immediately behind the sternum in the central thoracic cavity (mediastinum), positioned between the two lungs with only thin layers of pleura and pericardium separating these organs—making them intimately adjacent structures that share the confined thoracic space. 1
Spatial Relationship and Boundaries
The heart occupies the middle mediastinum with specific anatomical boundaries:
- Superior border: The heart extends from approximately the sternal notch (2nd intercostal space) 2
- Inferior border: Down to the xiphoid process (5th-6th intercostal space) 2
- Lateral borders: The cardiac silhouette spans toward the nipples bilaterally 2
- Anterior position: The heart sits directly posterior to the sternum, requiring probe angulation almost parallel to the horizontal plane when imaging from below 1
Proximity and Physical Contact
The lungs and heart are extremely close—essentially in direct contact:
- The heart and lungs are elastic structures sealed together within the expandable thorax, creating mechanical interactions between these organs 3
- Both organs are confined within the thoracic cavity, making their structural and functional association intimate 4
- The right ventricle lies immediately adjacent to lung tissue, while the left ventricle is positioned more posteriorly 1
- Only the pericardium (heart's outer covering) and pleura (lung's outer covering) separate these organs—thin membrane layers that allow direct mechanical influence 5
Clinical Implications of This Proximity
The close anatomical relationship creates significant physiological interdependence:
- Changes in lung volume and intrathoracic pressure directly affect cardiac filling and output through external constraint on the heart 5
- Pulmonary hyperinflation (emphysema, mechanical ventilation) can compress cardiac windows and limit ventricular filling 1, 5
- The negative pressure environment of the intact thorax is shared by both organs, creating dynamic interactions throughout the respiratory cycle 6
- Blood volume redistribution between pulmonary and cardiac chambers occurs continuously based on respiratory phase 5
Imaging Perspectives
From ultrasound imaging windows, the spatial relationships become evident:
- Parasternal views: The heart is accessed through the 3rd-5th intercostal spaces immediately left of the sternum, with lung tissue flanking both sides 1
- Subcostal views: The liver serves as an acoustic window because lung air would otherwise obscure the heart 1
- Apical views: Obtained at the point of maximal impulse (typically 5th intercostal space), where the cardiac apex approaches the chest wall between lung fields 1
Common pitfall: Patients with pulmonary hyperinflation have poor parasternal acoustic windows because expanded lung tissue interposes between the transducer and heart, demonstrating how minimal the normal separation is 1