The eustachian valve is an embryologic remnant of the valve of the inferior vena cava. It may be prominent in some individuals, but the echocardiographic appearance of a divided right atrium, as the consequence of a large eustachian valve, is extremely rare. Herein we describe an unusual giant eustachian valve with an echocardiographic appearance of a septal structure dividing the right atrium into 2 separate chambers. This abnormality should be differentiated from cor triatriatum dexter a very rare cardiac malformation for which it could be mistaken.