Nagarajan is fully trained in paediatric and adult congenital cardiac surgery. He is surgical lead for the thoracic, tracheal surgery, paediatric lung transplantation and surgical ECMO service. He is also honorary academic senior lecturer at University College of London. Nagarajan performs paediatric and neonatal cardiac and thoracic surgery and performs more than 75% of complex airway reconstructions of world-wide volume, including the only three tracheal transplantations performed so far in children. He is the Founder Member for many Associations worldwide and serves as committee member in NHS BT for Paediatric National organ donation committee member as well as clinical trials committee. He also serves as advisory committee member for National Wilms Tumour Panel in UK for complex Wilms tumour. He is also the scientific advisor and proctor/mentor for transplantation and mechanical support programme for Heart and lung transplantation service in Malaysia and Singapore as well as advisor for review of heart and lung transplantation in New Zealand and Australia. Nagarajan is a board member for International Society of Heart Lung Transplantation Journal, and Work Planning Committee Member and Regional Surgical Advisor for Royal College of Surgeons of Edinburgh for London. Nagarajan performs surgery in many European countries as part of service provision as well as for teaching purposes. He holds visiting professorships in many universities, including The University of Rotterdam in Netherlands, University of Leuven in Belgium, University of Graz in Austria and PGI, Chandigarh in India. He also conducts charity cardiac surgery program every year in South India for children who are in need of surgery for correcting congenital heart defects.