Tendon of valve of inferior vena cava

The tendon of valve of inferior vena cava or tendon of inferior pyramidal space (Tendon of Todaro) is a fibrous structure in the right atrium of the heart, formed by the confluence of the Eustachian valve and the Thebesian valve, that extends to the central fibrous body of the heart.

It is classically described as forming one of the borders of the triangle of Koch, an important anatomical landmark for locating the atrioventricular (AV) node during electrophysiological procedures. Histological studies have shown that the tendon is composed primarily of collagen and is present in most hearts, although its size, number, and prominence can vary, and it may be absent or duplicated, particularly in adults.

While the tendon is not directly visible during procedures, its anatomical course is used as a surrogate marker for the location of the AV node. However, some anatomical studies have questioned the reliability and constancy of the tendon as a landmark, noting significant variability and suggesting that other anatomical features may be more consistent for clinical orientation.

Note from author: in Terminologia Anatomica 2, the preferred term for the "tendon of Todaro" is "tendon of inferior pyramidal space". This choice is quite strange because this tendon is located into the triangle of atrioventricular node (triangle of Koch) and not really in the inferior pyramidal space (defined in the TA2 as the fibro-adipose tissue of the inferior atrioventricular groove, which fills the space between the atrial floor of the atrioventricular nodal triangle (triangle of Koch) and the crest of the muscular interventricular septum).