Objectives (1) To assess how main pulmonary artery peak Doppler velocity (MPAVpeak) correlates with right ventricular output (RVO) and superior vena cava flow (SVCf), (2) to assess the reproducibility of MPAVpeak and (3) to test the prognostic accuracy of MPAVpeak to predict high-grade intraventricular haemorrhage (IVH) or death at seventh day of life. Design Prospective cohort study. Setting Nine third-level neonatal units in Spain. Patients Preterm infants <33 weeks of gestational age who had standardised measurements of MPAVpeak, RVO and SVCf at 6, 12 and 24 hours of life. Main outcome measures High-grade IVH or death at seventh day of life. Results One hundred and ninety preterm infants with a median (IQR) gestational age and birth weight of 29.7 weeks (27.1–31.8) and 1152 g (892–1491), respectively, were included. High-grade IVH or death at seventh day of life occurred in 24 (12.6%). MPAVpeak was strongly correlated with RVO (Spearman rho 0.826–0.843). MPAVpeak discriminated well