Cardiac surgery is a critical intervention for a variety of cardiovascular conditions, yet it can frequently results in a spectrum of postoperative complications. Amongst various morbidities, Post-Operative Pulmonary Complications (POPCs) represent a significant clinical challenge leading to adverse outcomes like increased morbidity, mortality, and raised healthcare expenditures. The diaphragm, as the principal respiratory muscle, plays a pivotal role in maintaining pulmonary function. Diaphragmatic dysfunction (DD) in the perioperative period of Cardiac surgery has an incidence of up to 20%. Understanding the impact of DD on postoperative pulmonary function is imperative for optimizing patient care and clinical outcomes. Its occurrence has been linked to a spectrum of respiratory complications, ranging from pneumonia to difficulty in weaning from mechanical ventilation. In recent years, the advent of point-of-care ultrasonogram (POCUS) has emerged as a promising modality for real-time monitoring of DD. It offers a more accessible and feasible approach compared to traditional methods, providing immediate feedback on diaphragmatic movement, and facilitates timely intervention. Ultrasound has been used to assess Diaphragmatic Inspiratory Amplitude (DIA) (the expansion of the diaphragm when breathing). DIA has been shown to decrease in the post-operative period after cardiac surgery, which has been well-correlated with the occurrence of POPCs, however, its predictive value has not yet been studied in a cohort of cardiac surgical patients. Hence, we aim to address this gap by exploring the utility of DIA measured by ultrasonogram as a predictive tool in anticipating the occurrence of POPCs. We hypothesize that DIA can predict the occurrence of POPC in cardiac surgical patients. We will recruit 130 patients at University Hospital, London Health Science Centre, to this prospective, observational study.