The heart is a hollow, muscular egg-shaped organ which lies within median mediastinum
between the two arterious series circles, that is, pulmonary and systemic circles. It consists
of two separate sections: the right section connected with the pulmonary circle and filled
with venous blood and the left section connected with the systemic circle and filled with
arterious blood. Moreover, each section is subdivided into two cavities, the atrium and the
ventricle, separated from each other by a special valve apparatus. According to the heart
axis direction, anteriorly and leftwards caudally obliqued, the right atrium (RA) and the
right ventricle (RV) are located anteriorly in relation to the left atrium (LA) and the left
ventricle (LV). LA is the more cranial and posteriorly located cardiac chamber. The heart
within the mediastinum is contiguous to large vessels (aorta, pulmonary artery, and venae
cavae) and its pericardial sac presents adherences to diaphragm, sternum, dorsal column,
and mediastinal pleura.
The heart surface is “ carved ” by grooves outlining the four cavities; the atrioventricular
groove, perpendicular to the longitudinal axis, separates atrial from ventricular cavities,
whereas the anterior and the posterior longitudinal grooves define the border line between
the two ventricles. A surface limit between the two atria is recognizable at the diaphragm level.
Here one can recognize the interatrial groove. The two ventricles, characterized by a pyrami-
dal shape and based on the atrioventricular groove, represent a major part of the surface of
the heart. The most dorsal region, instead, represents a smaller portion of the heart. This is
posteriorly convex and has an irregular outline due to systemic venous structures (venae cavae
draining into RA) joining pulmonary ones (pulmonary veins draining into LA).
Figure 2.1 Three-dimensional ( 3-D ) volume rendering ( VR ) image. The figure depicts the left atrium with contiguous mediastinal structures. SCV superior caval
vein, DAO descending aorta, PA pulmonary artery, LA left atrium, LV left ventricle
The atria have a “ dome-like ” shape with appendages projecting forward and partially
surrounding the aorta origin, on the right, and the pulmonary artery, on the left. RA, cov-
ering the omolateral ventricular base, from which it is separated by the tricuspid valve,
hosts the venae cavae sinus in its posterior and median portion. The coronary sinus (CS)
outlet, draining blood flowing back from coronary circulation, is located relatively to RA
Figure 2.2 a 3-D VR image. LA posterior surface. Atrial anatomy and venous branching by reformatted images with external surface visualization. b 3-D maximum intensity project ( MIP ) image. LA posterior surface. Atrial anatomy and venous branching by reformatted images with high-density
pixel exaltation (angiographic view)
diaphragmatic wall and anteromedially on the left of the inferior vena cava opening. LA,
overlapping the omolateral ventricular base, shows, instead, a morphology that stretches
out crosswise while receiving pulmonary veins (PVs) outlet into its posterosuperior wall
(Figs. 2.1 and 2.2 ). The two atria show thin walls, with a common wall defined as interatrial
septum (IAS), about 2.5 mm thick. It is made of a muscular and a membranous portion,
the latter of which is located within the fossa ovalis region where thickness is lower.
