There have been suggestions made recently that our understanding of the atr
ioventricular junctions of the heart is less than adequate, with claims for
several new findings concerning the arrangement of the ordinary working my
ocardium and the specialised pathways for atrioventricular conduction. In r
eality, these claims are grossly exaggerated. The structure and architectur
e of the pathways for conduction between the atrial and ventricular myocard
ium are exactly as described by Tawara nearly 100 years ago. The recent cla
ims stem from a failure to assess histological findings in the light of cri
terions established by Monckeberg and Aschoff following a similar controver
sy in 1910. The atrioventricular junctions are the areas where the atrial m
yocardium inserts into, and is separated from, the base of the ventricular
mass, apart from at the site of penetration of the specialised axis for atr
ioventricular conduction. There are two such junctions in the normal heart,
surrounding the orifices of the mitral and tricuspid valves. The true sept
;al area between the junctions is of very limited extent, being formed by t
he membranous septum. Posterior and inferior to this septal area, the atria
l myocardium overlies the crest of the ventricular septum, with the atrial
component being demarcated by the landmarks of the triangle of Koch. The ad
jacent structures, and in particular the so-called inferior pyramidal space
, were accurately described by McAlpine (Heart and Coronary Arteries, 1975)
. Thus, again there is no need for revision of our understanding. The key t
o unravelling much of the alleged controversy is the recognition that, as i
ndicated by Tawara, the atrioventricular node becomes the atrioventricular
bundle at the point where the overall axis for conduction penetrates into t
he central fibrous body. There are also marked differences in arrangement,
also described by Tawara, between the disposition of the conduction axis in
man as compared to the dog. Anat Rec 260:81-91, 2000. (C) 2000 Wiley-Liss,
Inc.