Coronary artery aneurysms (CAAs) are rare findings caused by atherosclerosis in about 50% of cases. They are usually diagnosed using coronary angiography, cardiac computed tomography, or magnetic resonance imaging. In this report, we present a rare case of giant, isolated right CAA, detected by transthoracic echocardiography in an adult patient with unstable angina. Diameters of the aneurysm were 3.6 cm × 2.7 cm. Anterior-septal hypokinesia of the left ventricle was also noted. A comprehensive echocardiographic examination, including contrast study, excluded alternative diagnoses and supported the hypothesis of a coronary ectasia. The coronary angiography confirmed the diagnosis of giant coronary aneurysm and revealed a severe three-vessel disease. The patient was treated with cardiac surgery a few days later: two coronary artery bypass grafts and exclusion of the aneurysm by surgical legation were successfully performed.