Small heart sign

The small heart sign represents a rarely encountered but critical sign on chest caused by a sudden reduction of heart size caused by cardiac tamponade due to either tension pneumopericardium or pneumomediastinum.

A sudden, >2 cm reduction in the transverse cardiac diameter is considered highly suggestive of tamponade. Unfortunately, the exact measurement necessitates the immediate availability of a recent, comparable prior radiograph. Nevertheless, it has been shown to be a helpful feature in following up on a known pneumopericardium/pneumomediastinum and aiding the prompt diagnosis of a developing tension component .