Small heart syndrome

A small cardiothoracic ratio (CTR) is defined as <42%/0.42 when assessed on a PA chest radiograph, and is often called small heart syndrome. A pathologically-small heart is also known as microcardia.
It can be due to/associated with a number of entities:

• adrenal insufficiency, e.g. Addison disease
• heart transplant
• cachectic state 
  • advanced age
  • malnutrition
  • bulimia nervosa
  • anorexia nervosa
  • advanced malignancy
• asthmatic paroxysm with emphysema
• constrictive pericarditis
• myalgic encephalomyelitis/chronic fatigue syndrome​ (ME/CFS)
• physiological factors: e.g. Valsalva maneuver

Siehe auch:

• cardiothoracic ratio
• Pericarditis constrictiva