To identify the measures of biventricular function and surrogates of pulmonary vascular resistance that can be expected in relatively stable extremely premature neonates, and evaluate maturational changes in myocardial performance in this patient population.

This was a prospective observational study. Clinically stable extremely preterm newborns were divided into 3 cohorts based on gestational age: cohort 1 (24^0/7–25^6/7 weeks), cohort 2 (26^0/7–27^6/7 weeks), and cohort 3 (28^0/7–29^6/7 weeks). Serial echocardiograms were obtained on day of life 3-5, 7-10, and just prior to discharge.

In total, 46 subjects met the criteria aimed at capturing only the most clinically healthy and stable newborns less than 29^6/7 weeks of gestational age. Myocardial performance was reliably assessed by echocardiography with high inter-reader correlation. Normative values were identified for right ventricular function, left ventricular function, and surrogates of pulmonary vascular resistance.

Biventricular systolic performance is significantly different in the clinically stable extremely premature neonate when compared with healthy full-term newborns. All participants had evidence of poor biventricular compliance at birth which improved with maturation. Extreme prematurity does not appear to adversely affect myocardial functional maturation at the time of term corrected age and/or discharge.