Down syndrome (DS) is the commonest chromosomal abnormality of live born infants globally with an incidence of 1:444 live births in Ireland. One of the major morbidities associated with this diagnosis is congenital heart disease (CHD) and pulmonary hypertension (PH). The presence of PH in infants with DS is associated with significant morbidity and an increase risk of mortality. Infants with DS are at a significantly higher risk of requiring extra-corporal membrane oxygenation (ECMO) due to respiratory failure than the general infant population (up to 6 fold). The impact of the diagnosis of DS, the presence of CHD and the associated PH on myocardial function during transition and over the first 2 years of age in this population is poorly understood and warrants further study. In particular, serial measurements of pulmonary pressures in this population over the first week of age are lacking. In this study we will use novel methods of functional assessment to better characterise myocardial function in infants with Down syndrome during the transitional period (over the first week of age) and throughout the first two years of age. The newer methods of functional assessment will include: tissue Doppler imaging (TDI) and tissue Doppler-derived deformation analysis; speckle tracking echocardiography (STE) to measure deformation and left ventricular (LV) rotational mechanics; right ventricle (RV) specific parameters including fractional area change (FAC) and tricuspid annular plane systolic excursion (TAPSE). Further evaluation of cardiac performance in DS infants with and without CHD may yield more insight into the pathophysiology of cardiac dysfunction and pulmonary hypertension that are recognised features in these patients. This could aid in our ability to monitor and treat patients, as well as improve our ability to predict outcomes.