It could be pulmonary Edema: If the heart is not pumping efficiently after surgery, fluid can back up into the lungs. Coughing that worsens when lying flat is a classic sign of fluid in the lungs (orthopnea), as gravity causes the fluid to spread across a larger surface area of the lungs. The patient is already on Dytor Plus, a diuretic used to manage fluid levels. It could be pleural effusion: It is common for fluid to collect in the space around the lungs after CABG. This can irritate the lungs and cause a persistent dry cough Your patient is not on any ace inhibitors. They can cause cough. Please double check if he is taking any ace inhibitors like Ramipril or enalapril