Cardiovascular impact of dexamethasone (Dex), is not well understood. Most data used a six-week, high-dose regimen, and is limited to findings of hypertension and cardiac hypertrophy. This study ascertained the impact of low-dose Dex on cardiac indices, when administered to extremely preterm infants for lung disease. A pre-post intervention prospective echocardiographic (Echo) study was undertaken, with cardiac assessments performed before and within 24 hours after completion of first course of therapy (10 day regimen, cumulative 0.89mg/kg). 30 infants with gestation and birthweight 24.6±1.1 weeks and 612±125g respectively, were studied. The age at Dex administration was 20±9 days. Fractional inspired oxygen decreased from 0.7±0.23 to 0.35±0.14, P<0.001. Patent ductus arteriosus was noted in 20 infants at Echo1. At Echo2, the ductal size diameter decreased from 2.16±0.8 to 1.1±0.8mm, P=0.0003, with complete closure in 7/20 (35%). Reduction in left pulmonary artery end-diastolic velocity was noted (17±12 to 9±10 cm/s, P<0.001). Pulmonary vascular resistance decreased (increased time to peak velocity/ right ventricular ejection time, 0.2 ± 0.03 to 0.23 ±0.03, P=0.0001) and right ventricular systolic performance improved (TAPSE, 4.9±0.8 to 5.5±0.9 mm, P=0.02). No significant changes in fractional shortening and left ventricular mass were noted. A significant increase in blood pressure was noted. As a percentage of pre-treatment baseline, the mean increase for systolic blood pressure was 20.3% (95% confidence interval = 14-26) on day 2 (P=0.008). Low-dose Dex influenced ductal calibre and pulmonary vascular resistance.