We present our single-center results of paediatric patients who underwent surgical ASD II closure via lateral thoracotomy. Retrospective analysis. Patients were divided into a cardiac arrest group and a cardiac fibrillation group. All procedures were performed via right midaxillary thoracotomy through a single incision without side ports. All 37 consecutive patients between 03/2019 and 08/2022 (median age 3 years; percentile 25th: 2; 75th: 5 years) in both groups were free of mortality and postoperative morbidity such as haemodynamically relevant residual shunt or malignant arrhythmias. Cardiopulmonary bypass time was significantly shorter in the fibrillation group (mean: 34.7 min. Vs 52.6 min., p 0.01), all patients were weaned off the ventilator immediately postoperatively. Length of ICU stay was not different between the two groups. Postoperative hospital stay was significantly longer in patients with cardiac arrest (mean: 5.6 days vs 4.9 days, p 0.04). Postoperative laboratory parameters did not differ between the two groups. All patients were discharged with normal left ventricular function and normalized cardiac enzymes. Minimally invasive closure of an atrial septal defect during atrial fibrillation is a safe procedure with results comparable to those of an induced cardiac arrest procedure.