A 55 year old, diabetic, hypertensive female patient diagnosed with rheumatic heart disease and severe mitral stenosis was posted for mitral valve repair surgery. She was a known case of hypothyroidism with seizure disorder. On 2D echo, she had a severely dilated left atrium and a moderate degree of pulmonary hypertension (RVSP 48 mm Hg) She was found to have a left atrial clot on the Trans Esophageal Echocardiography (TEE) performed prior to surgery. On clinical examination, the patient was obese and a candidate for difficult airway. Her pulse was irregularly irregular suggestive of atrial fibrillation which was confirmed on ECG. Patient was taken up for surgery under high-risk with all surgical and anesthetic concerns explained to the family. Although there were no events intraoperatively, patient was difficult to wean off the ventilator postoperatively with one episode of cardiac arrest during a weaning trial. Patient was successfully revived after CPCR as per AHA guidelines. After an elective tracheostomy was performed, various causes of the sudden ventilator dependency that were ruled out included cor pulmonale owing to pulmonary hypertension, an undetected preoperative obstructive sleep apnoea, embolization of the clot to the brain, and chronic hypothyroidism leading to respiratory muscle weakness.