Left ventricular output (LVO), left pulmonary artery blood flow (LPA) and patency of the ductus arteriosus (PDA) were studied with 2D/pulsed Doppler ultrasound before, during and after phototherapy treatment in 27 preterm infants (gestational age < or =32 wk), who were exposed for a minimum of 12 h to phototherapy for non-haemolytic hyperbilirubinemia. In 14 infants (52%) the ductus arteriosus reopened during phototherapy, but ductal patency was not of haemodynamic importance. LVO initially decreased in preterm infants in whom the ductus did not reopen. From 12 h until discontinuation of phototherapy, LVO and LPA were higher than before phototherapy in all infants. After withdrawal of phototherapy, LVO and LPA returned to pre-phototherapy values.