Intraoperative formation of a cardiac thrombus is an exceedingly rare incident, and the cases described have occurred during liver transplantation and cardiac surgery (1–3). We present two cases of acute intracardiac thrombus formation diagnosed by transesophageal echocardiography during thoracoabdominal aortic aneurysm repair. Two patients, aged 75 yr and 60 yr, underwent repair of thoracoabdominal aortic aneurysms. Preoperative coagulation testing was within normal ranges, with the exception of fibrinogen in the first patient (716 mg/dL). In both cases heparin 5000 U was given before aortic cross-clamping. Distal aortic perfusion was with a modified Gott shunt in the first patient and via a temporary right subclavian artery to right femoral artery shunt in the second patient. Blood loss during aortic cross-clamping (2 and 5 L, respectively) was replaced with crystalloid, fresh-frozen plasma, and packed red blood cells. The patients were given protamine (25 mg and 50 mg), aprotinin (1,000,000 U in both cases), and platelet concentrates (4 U in both cases) after removal of the aortic cross-clamp. At this point, arterial blood pressure decreased (to approximately 40/20 mm Hg) despite administration of epinephrine (170 μg/min), requiring open chest cardiac compressions. Transesophageal echocardiography examination demonstrated intravascular thrombus formation in both patients. In the first patient, thrombi were noted in both atria as well as the aortic arch (Fig. 1; please see video loop available at www.anesthesia-analgesia.org). In the second patient, thrombi were observed to extend from the right atrium to the right ventricle (Fig. 2A). Further thrombi were observed on the aortic valve and inside the aortic graft (Fig. 2 B, C). In both patients, thrombolytic therapy with recombinant tissue plasminogen activator (10 mg IV) was initiated. Despite lysis of thrombi, cardiac dysfunction persisted and both patients died in the operation room.Figure 1.: Intraoperative transesophageal echocardiography obtained subsequent to the repair of a thoracoabdominal aortic aneurysm and declamping of the aorta in case 1. The four-chamber view shows a giant thrombus in the left atrium (LAT) and a further thrombus in the right atrium (RAT). LV, left ventricle; RV, right ventricle.Figure 2.: The transesophageal echocardiographies were obtained after declamping of the thoracoabdominal aortic aneurysm in case 2. A, the four-chamber view demonstrates a large intracardiac thrombus (T) extending from the right atrium (RA) to the right ventricle (RV). No thrombus formation was detectable in the left atrium (LA) or left ventricle (LV). B, thrombus formation at the aortic valve shown in the midesophageal aortic valve long axis. C, thrombus formation in the aortic prosthesis demonstrated in the descendent aortic short axis.There have been several reports of acute intracardiac thrombus formation during cardiac surgery (1,2) and liver transplantation (3). The etiology was thought to be multifactorial, resulting from low-flow state, use of antifibrinolytics, heparin-protamine reversal, antithrombin III deficiency, factor V Leiden abnormality, and massive transfusion of hemostatic blood products. In this report there are several possible explanations for the development of intravascular thrombus, including transfusion of platelets and fresh-frozen plasma, the use of aprotinin, low-flow state, and the possibility of preexisting thrombophilia. The fact that the diagnosis would certainly have been missed without transesophageal echocardiography underlines its potential to diagnose even unexpected causes of hemodynamic disturbances.