Lung hyperinflation is a technique used by physiotherapists to mobilize and remove excess bronchial secretions, reinflate areas of pulmonary collapse and improve oxygenation. To assess the efficacy of manual hyperinflation in improving arterial oxygenation (PaO2) of paediatric patients with upper lobe lung collapse after cardiac surgery. 18 paediatric patients who had undergone heart surgery and having upper lobe collapse in the post-op ventilation period underwent Manual Hyperinflation (MH). Parameters included arterial oxygen tension (PaO2) value in ABG analysis, clinical findings such as collapsed upper lung lobe in chest radiograph and air entry in auscultation were collected before and 30 min post MH session and documented. The patients were treated with manual hyperinflation delivered using a pediatric AMBU bag with pressure of about 40 cm H2O. Four sets of eight bag compressions with inflation rate of 10 breaths per minute were delivered during each manual hyperinflation. The result showed that there was a significant improvement in arterial oxygenation (PaO2) by administering manual hyperinflation therapy for the upper lobe collapse in post-op ventilated paediatric patients. In this study, it is evident that manual hyperinflation is an effective technique in management of Lung collapse (upper lobe) in post-op pediatric patients. This clearly demonstrates that further research in this area is warranted.