Cardiomegaly is seen in –
Causes of Cardiomegaly 
Myocardial disease

Endocardial fibroelastosis                              o Glycogen storage disease
Myocarditis (viral or idiopathic)

Coronary artery diseases resulting in myocardial insufficiency

Anomalous origin of the left coronary artery from the pulmonary artery
Collagen disease (periaarteritis nodosa)
Kawasaki disease

Congenital heart defect with severe heart failure
Miscellaneous conditions

Congestive heart failure (CHF) secondary to respiraoty disease (upper airway obstruction, bronchopulmonary dysplasia)
Supraventricular tachycardia with CHF
Pericardial effusion
Tumors of the heart
Severe anemia
Endocrine disorders (thyrotoxicosis, pheochromocytoma)
Malnutrition (beriberi, kwashiorkor, carnitine deficiency)
Sensitivity/toxic reactions (sulmonamides, doxorubicin)
Muscular dystrophies
Familial dilated cardiomyopathies
Multivalvular disease
Anemia
Pericardial effusion
All of these