OBJECTIVE:Umbilical vein catheterization (UVC) is a frequently performed procedure in neonatal intensive care units, which has significant complications. Arrhythmia is one of the most complication of this procedure.This study has been planned to determine whether placement of or drug administration through umbilical vein catheters result in cardiac arrhythmias.MATERIALS AND METHODS: This study has been carried out on 61 newborns receiving medical care in the Neonatal Intensive Care Unit of Kocaeli University Faculty of Medicine Hospital utilizing 24-hour Holter monitoring. Of the infants enrolled, 30 had been placed an umbilical vein catheter. Thirty-one infants without catheters were taken as the control group.RESULTS: No significant difference has been found between the infants with catheters and those without in terms of min., mean and max.heart rate, premature atrial contraction, premature ventriculary contraction, supraventricular tachyarrhythmia, pause, bradycardia, and sudden drops in heart rate. No ventricular tachycardia and no atrio-ventricular block were detected. Two infants with catheters and one infant in the control group had transient wondering atriyal rhythm. CONCLUSION:In conclusion,our study shows that umbilical vein catheters do not pose a risk for cardiac arryhthmias when positioned properly, as was the case in all our patients.this study showed us that be can avoid any arrhythmias if umbilical catheters were positioned properly as ordered and fluid and drug therapies applicated properly and carefully. We recommend cardiac monitorization of all infants during a UVC procedure.