On defining microcardia: application in pulmonary emphysema.

Pulmonary emphysema was the disease entity from which we derived a definition for microcardia in males. After the fourth decade, a cardiothoracic ratio of 38% or less is considered to represent a small heart. Among male Veterans Hospital patients between the ages of 41 and 83, the probability of an individual without emphysema having a cardiothoracic ratio of 38% or less was under 1%. Microcardia, even as an isolated sign, should make one suspect strongly the presence of subclinical emphysema and to consider instituting a prophylactic regimen. Hearts should be measured to judge not only increased size but decreased size in both patient and examinee groups.