In patients with cyanotic congenital heart disease (CCHD), the risk of thromboembolic events is increased due to the presence of abnormal anatomy with dilated and dysfunctional cardiac chambers, intracardiac shunting and cardiac arrhythmias. In addition, it has been postulated that abnormal erythrocytosis and hemostatic abnormalities might contribute to a pro-thrombotic state. In a cross sectional study of 98 clinically stable adults with CCHD, Jensen and colleagues (see page 1540) found evidence for cerebral thrombosis in 47% on imaging although only 22% had a clinical history of a cerebral event. The difference between imaging and clinical history was less striking for pulmonary thrombosis, seen by imaging in 31% of patients, compared to a clinical history of an event in 25%. In this cohort, the complexity of CCHD and low oxygen saturations were associated with an increased prevalence of cerebral thrombosis while age was the only factor associated with pulmonary thrombosis. There was no association between thrombosis and the degree of erythrocytosis, hemostatic abnormalities, chronic anticoagulation, arrhythmias, or previous heart surgery (figure 1).