Chylothorax is a recognized complication of intrathoracic surgery, but its occurrence after coronary artery bypass grafting (CABG) is very rare. We report a case of a fatal pulmonary embolism as a complication of chylothorax following CABG. The patient was an 82-year-old woman who presented with increasing chest pain 2 weeks after discharge after an uncomplicated CABG. A computerized tomography (CT) scan with contrast angiogram showed a left-sided pleural effusion and no concurrent pulmonary embolus. Analysis of the pleural effusion revealed a chylothorax, which was treated with chest tube drainage and total parenteral nutrition followed by an oral medium-chain fatty acid diet. The patient improved steadily but, on day 6, she developed acute hypoxemic respiratory failure and shock. A CT angiogram revealed a massive pulmonary embolus and, despite thrombolysis, the patient died. Autopsy confirmed an acute saddle embolus in the pulmonary trunk. The patient had received appropriate venous thromboembolism prophylaxis with subcutaneous unfractionated heparin during her hospital course. This is the first reported case of a fatal pulmonary embolism that occurred in the setting of a post-CABG chylothorax in adults. The occurrence of this complication despite unfractionated heparin thromboprophylaxis may suggest a role for other, more effective medications, such as low molecular weight heparin or fondaparinux in patients with chylothorax.