The sinotubular junction (STJ) is a well-defined circular ridge found between the superior or tubular segment of the ascending aorta and the inferior, bulbous segment of the ascending aorta, known as the aortic root.
The sinotubular junction is the region of the ascending aorta between the aortic sinuses (of Valsalva) and where the normal tubular configuration of the aorta is attained.