OBJECTIVE To study the effects of hypothermia on cardiac function in neonates after birth asphyxia. METHODS Fifty term newborns with Apgar score < 5 at 5 minutes were randomly divided into no cooling group (normothermia group, NG; rectal temperature = 36.5 degrees C +/- 0.5 degrees C, n = 27) and cooling group (hypothermia group, HG; rectal temperature = 34.5 degrees C +/- 0.3 degrees C, nasopharyngeal temperature = 34.0 degrees C +/- 0.5 degrees C, n = 23). The selective head cooling was applied to maintain nasopharyngeal temperature at 34 degrees C for 72 h in hypothermia group. Systolic and diastolic function was detected at the end of treatment by echocardiogram. RESULTS (1) The heart rate was obviously decreased during the hypothermia treatment, and there was a significant difference between HG and NG [(103 +/- 15) bpm vs. (126 +/- 14) bpm, P < 0.05]. No cardiac arrhythmia and hypotension were found in all neonates. (2) There were no significant differences on the ejection fraction, stroke volume and cardiac output of left ventricle between the two groups (P > 0.05). No significant difference was found in the numbers of left and right ventricular diastolic dysfunction, pulmonary hypertension between the two groups (P > 0.05). (3) The level of cardiac troponin T (cTnT) in plasma was (0.47 +/- 0.15) ng/ml in HG, and (0.35 +/- 0.21) ng/ml in NG, and there was no significant difference between the two groups (P > 0.05). CONCLUSIONS No significant cardiac dysfunction complication caused by the hypothermia treatment was found in term neonates after birth asphyxia.