Duplication of superior vena cava (SVC) is a rare anomaly. The incidence of double SVC in general population is 0.3% whereas in patients with congenital heart disease it varies between 10-11%. Double SVC cases have clinical importance if especially the one on the left side drains into the left atrium. Moreover, double SVC is surgically important in the presence of congenital heart disease. In this article, we presented adult patients who incidentally diagnosed with double SVC, one drained into the right atrium while the other into the left atrium and discussed the embryologic basis of these patent vessels.