Interventional cardiac catheterization in children and adolescents is traditionally performed with the patient under general anesthesia and endotracheal intubation. However, percutaneous closure of atrial septum defect (ASD) without general anaesthesia is currently being attempted in a growing number of children. The study objective was to evaluate the success and complication rate of percutaneous ASD closure in spontaneously breathing children under deep sedation. Retrospective single centre cohort study of consecutive children undergoing percutaneous ASD closure at a tertiary care pediatric cardiology centre. Transesophageal echocardiography (TEE) and percutaneous ASD closure were performed with the patient under deep sedation with intravenous bolus of midazolam and ketamine for induction and propofol continuous infusion for maintenance of sedation in spontaneously breathing children. One hundred and ninety-seven patients (median age 6.1 years [minimum 0.5; maximum 18.8]) underwent TEE and ASD balloon sizing. Percutaneous ASD closure was attempted in 174 patients (88 %), and device implantation was performed successfully in 92 %. To achieve sufficient deep sedation, patients received a median ketamine dose of 2.7 mg/kg (0.3; 7) followed by a median propofol continuous infusion rate of 5 mg/kg/h (1.1; 10.7). There were no major cardiorespiratory complications associated with deep sedation, and only two patients (1 %) required endotracheal intubation due to bronchial obstruction immediately after induction of sedation. Seventeen patients (8 %) had minor respiratory complications and required frequent oral suctioning or temporary bag-mask ventilation. TEE and percutaneous ASD closure can be performed safely and successfully under deep sedation in spontaneously breathing children of all ages.