Minimally invasive cardiac surgery (MICS) in pediatric patients remains an emerging field with limited applications in developing countries. This case report describes the successful application of lower partial sternotomy for atrial septal defect (ASD) closure in a 4.5-year-old boy weighing 16 kg. The patient presented with a history of recurrent respiratory tract infections and was diagnosed with ostium secundum type ASD with moderate pulmonary arterial hypertension. Due to deficient inferior rims, device closure was contraindicated, necessitating surgical intervention. The entire procedure was performed through a single midline lower partial sternotomy incision without the need for a groin incision for cardiopulmonary bypass (CPB), making this the first reported case of such technique in a pediatric patient in South Tamil Nadu. The procedure demonstrated significant advantages including reduced postoperative pain, early mobilization, shorter hospital stay, and preservation of chest wall integrity for future cardiac interventions. This case highlights the feasibility and benefits of MICS in carefully selected pediatric patients when performed by experienced surgeons.