Dexamethasone is now frequently used in the treatment of bronchopulmonary dysplasia. We report on two premature babies receiving dexamethasone who developed symptomatic myocardial hypertrophy and left ventricular outflow tract obstruction, as documented by M-mode echocardiography and Doppler studies. A normal heart was recorded on echocardiography before and after dexamethasone treatment. The patients had no known risk factors associated with the development of obstructive hypertrophic cardiomyopathy.