Despite the use of exogenous surfactants, the incidence of bronchopulmonary dysplasia (BPD) has not decreased as much as expected. Of 208 newborns involved in trials with Exosurf at our center, 51 had BPD. Among these newborns, 8 were found retrospectively to have secondary worsening of respiratory distress syndrome after initial improvement with surfactant treatment. Oxygen requirements decreased from 89 +/- 15% to 58 +/- 16% (mean +/- SD), respectively, before and 48 h after surfactant, and then reached a plateau of 34 +/- 10% before dramatic deterioration at 22 +/- 9 days of life. The patients had signs of cardiac failure and increased oxygen requirements of up to 76 +/- 19% within 6 h. A patent foramen ovale (PFO) was demonstrated at echocardiography with a left to right shunt at Doppler. No other cause of worsening was found. Five infants had significant improvement when treated with digoxin and furosemide. This retrospective study raises questions about the relationship between PFO and BPD that should be explored in a prospective study.