[Tendon of Todaro in the human heart]

The material consists of 50 human hearts without either pathological changes or congenital malformations. Macroscopic and microscopic methods were applied. Histological specimens were stained alternatively with hematoxylin-eosin and according to van Giesson and Masson. In each heart the tendon of Todaro was dissected from its portion situated between the inferior vena cava and coronary sinus up to central part of the membranous septum (Fig. 1). The hearts were divided into 3 groups according to age: fetuses (20 hearts), infants (15) and adults (15) (Table I). In all hearts of fetuses and infants the tendon of Todaro was found to be a well-developed cylindrical structure covered with endocardium. In histologic specimens the tendon was s solid structure well-separated from other tissues (Fig. 3, Fig. 4). In hearts of adults (17-45 years old) the tendon of Todaro was less evident. However, in histological specimens it was present as a compact connective tissue band (Fig. 2). In hearts of subjects older than 50, the endocardium of this area was not elevated and not distinguishable even by palpation. The connective tissue band was formed by rather dissipated fibres, poorly separated from surrounding structures. As a result of our study one may conclude that the tendon of Todaro is present in each human heart. It is well-developed in hearts of fetuses and infants. Later it diminishes gradually becoming almost inconspicuous in old subjects.