Dissecting aortic aneurysms and pseudoaneurysms of the ascending aorta can occur secondary to clamping of the ascending aorta, incision of the great vessels, or secondary to aortic cannulation for cardiopulmonary bypass. Contrast-enhanced CT offers an excellent means of distinguishing between aortic pathology and other causes of mediastinal widening following cardiac surgery. Five cases are reported in which iatrogenic vascular lesions were identified on CT as the cause of postoperative mediastinal widening.