To determine the cardiac output change in neonates who were under nasal continuous positive airway pressure (CPAP) therapy, eleven newborn neonates, who were admitted to our neonatal intensive care unit with respiratory diseases, were enrolled in the study. Cardiac output was measured by pulsed Doppler echocardiogram at various pressures of 0, 2, 4, 6, 8, and 10 cm H2O and revealed 301 +/- 47, 300 +/- 49, 289 +/- 55, 275 +/- 64, 269 +/- 59 and 242 +/- 50 ml/min/kg, respectively. Cardiac output depressed significantly between 0 cm H2O and 8 cm H2O (P = 0.025), and between 0 cm H2O and 10 cm H2O (P = 0.004). We conclude that cardiac output may be depressed in neonates who are under high levels of nasal CPAP therapy, and suggest that high levels of nasal CPAP therapy must be used with caution, especially when the therapy is applied to the low birth weight neonates.