Max limit of cardiothoracic ratio in chidren below 2 years:

Explanation: Measurement of the cardiothoracic (CT) ratio is by far the simplest way to estimate the heart size in older children. The CT ratio is obtained by relating the Largest transverse diameter of the heart to the widest internal diameter of the chest. CT ratio = (A + B) ÷ C where A and B are maximal cardiac dimensions to the right and left of the midline, respectively, and C is the widest internal diameter of the chest. A CT ratio of more than 0.5 indicates cardiomegaly. The CT ratio cannot be used with accuracy in newborns and small infants, in whom a good inspiratory chest film is rarely obtained. In this situation, the degree of inadequate inspiration should be taken into consideration. Also, an estimation of the cardiac volume should be made by inspecting the posteroanterior and lateral views instead of the CT ratio.