The natural history of CAA is largely unknown, as most reports in the literature involve only a small number of patients with relatively short-term follow-up. However, reported complications include thrombosis, embolization, rupture, fistula, vasospasm, and mass effect. Such a thrombus is prone to enlarge, which may cause occlusion of the aneurysm, or to dislodge and embolize to major distal vessels or the coronary microcirculation, leading to acute coronary syndrome. In cases with fistula formation, complications are congestive heart failure due to high output status and coronary artery steal phenomenon due to reduction in myocardial blood flow distal to the site of the coronary artery fistula. Furthermore, fistulae can cause flow turbulence and roughen the endothelium, leading to bacterial colonization and endocarditis. Hemoptysis, hemothorax, hemodynamic collapse, and death secondary to rupture of a giant CAA have also been reported. Finally, a mass effect on adjacent anatomic structures in the chest, causing compression of the cardiac chambers and the pulmonary artery, has also been reported.