the sa node is located in the wall (myocardium) of the right atrium, laterally to the entrance of the superior vena cava in a region called the sinus venarum (hence "sino-" + "atrial)". it is positioned roughly between a groove called the crista terminalis located on the internal surface of the heart and the corresponding sulcus terminalis, on the external surface. these grooves run between the entrance of the superior vena cava and the inferior vena cava.