Sternocostal Surface of the Heart — Formation and Chambers
Direction
The sternocostal surface faces forwards, upwards, and slightly to the left.
Formation
The sternocostal surface is formed by four cardiac chambers, in the following proportions:
| Chamber | Contribution | Location on Surface |
|---|---|---|
| Right ventricle | Largest — central and left portion | Forms the bulk of the surface |
| Right atrium | Right portion | Right border and right upper part |
| Left ventricle | Narrow strip — lower left margin | Between anterior interventricular groove and left border |
| Left auricle | Small upper left | Projects from behind the pulmonary trunk at upper left |
Left atrium is not visible on the sternocostal surface — it is completely hidden behind the ascending aorta and pulmonary trunk, which emerge from the base of the heart and cover it anteriorly.
Structures Appearing at the Upper Part
From right to left along the upper part of the sternocostal surface:
- Superior vena cava — right side, entering the right atrium
- Ascending aorta — central, emerging from the left ventricle behind the pulmonary trunk
- Pulmonary trunk — left of centre, emerging from the infundibulum of the right ventricle
- Right auricle — overlaps the root of the ascending aorta
- Left auricle — visible at the upper left margin, projecting from behind the pulmonary trunk
Anterior Covering Structures
The sternocostal surface is covered anteriorly by:
- Body of the sternum and costal cartilages 2–6
- Anterior borders of both lungs and their pleurae (covering most of the surface)
- A thin wedge of anterior mediastinum (fibrofatty tissue, thymus remnant)
Area of Superficial Cardiac Dullness
The cardiac notch of the left lung leaves a triangular area of the sternocostal surface not covered by lung — directly behind the left 4th and 5th costal cartilages and the adjoining sternum. Here, only the pericardium (without overlying lung) separates the chest wall from the right ventricle.
Percussion here gives dullness — the area of superficial cardiac dullness.
Disappearance of the area of superficial cardiac dullness suggests overexpansion of the left lung (emphysema) or left-sided pneumothorax — the lung has expanded into the costomediastinal recess and now covers the previously bare area.