A 67 years old nondiabetic, a hypertensive patient underwent off-pump quadruple CABG. On a first postoperative day, chest drains were removed and a chest x-ray revealed air under the right hemidiaphragm which was not seen in preoperative x-ray. Bedside ultrasound scan of the abdomen was normal and confirmed the findings of x-ray. The patient denied any discomfort in the abdomen.

Pre-operative and post-operative x-rays are displayed. What is the diagnosis?