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To assess myocardial function and presence of pulmonary hypertension (PH) using both tissue Doppler imaging (TDI) and conventional echocardiography in preterm infants of <32 weeks gestation with chronic lung disease (CLD).Prospective observational study.Tertiary neonatal intensive care unit.Three groups of preterm infants were recruited. Group 1—CLD receiving positive pressure airway support including high-flow humidified nasal cannula oxygen (n=25), group 2—CLD receiving low-flow nasal oxygen (n=25) and group 3—no CLD (n=22).Echocardiography was performed around 36 weeks corrected gestational age. Myocardial function and PH were assessed using both conventional (left ventricular fractional shortening (LVFS) and left ventricular output (LVO), tricuspid regurgitation and ventricular septal flattening) and TDI techniques (myocardial velocities, myocardial performance index (MPI) and right ventricular isovolumetric relaxation time (RV-IVRT)).The MPI of right ventricle (RV) and left ventricle (LV) was significantly higher in CLD infants: mean RV MPI group 1—0.79, group 2—0.65 and group3—0.52. LV MPI: group 1—0.77, group 2—0.70 and group 3—0.45. There was a trend towards higher MPIs in group 1 compared with group 2. LVFS and LVO were similar across all three groups. RV-IVRT was also significantly higher in infants with CLD infants (group 1—64 milliseconds, group 2—62 milliseconds and group 3—52 milliseconds). PH was not detected by conventional echocardiography.Infants with CLD have evidence of relative biventricular dysfunction and higher pulmonary arterial blood pressure as demonstrated by TDI, which were not detected by conventional echocardiography.