Anatomy of the Heart: Difference between revisions

==Position of the heart==

The long axis of the heart is at an angle to the long axis of the body. Approximately a third of the heart is to the right of the midline of the sternum and the remainder is to the left of the midline.

]]

'''A.''' Viewed from the front, the right atrium and right ventricle overlaps the left atrium and left ventricle. The atrial chambers are to the right of their respective ventricular chambers.

<br>'''B.''' The four cardiac valves are at different levels and different planes with the pulmonary(P) valve situated the most cephalad. The aortic(A) valve is wedged between the tricuspid(T) and mitral(M) valves.]]  

The cardiac silhouette is generally taken to be trapezoidal in shape. The rib cage provides good markers for charting the cardiac silhouette. The normal position of the cardiac apex is generally taken to be in the fifth intercostal space in the mid-clavicular line. The lower border is a nearly horizontal line in the area of the left sixth rib to the right sixth costal cartilage (Figure 2). The upper border is hidden behind the sternum at the level of the second and third cartilages. The right margin of the heart peeps out behind the right border of the sternum between the right third and sixth cartilages. In the infant, the upper part of the cardiac shadow is broad owing to the prominence of the overlying thymus gland.  

Inferior to the thymus, a fibrous pericardial sac encloses the mass of the heart. The sac has cuff-like attachments around the adventitia of the great arteries and veins as they enter or emerge from the heart. The pericardial cavity is contained between the double-layered serous pericardium. The parietal pericardium is adherent to the fibrous pericardium while the visceral layer is densely adherent to the cardiac surface forming the epicardium. Due to the contours of the heart and great arteries there exist two recesses within the pericardial cavity. These are the transverse and oblique sinuses. The transverse sinus occupies the inner heart curvature and lies between the posterior surface of the great arteries and the anterior surface of the atrial chambers. The reflection of the serous pericardium around the four pulmonary veins and the inferior caval vein forms the oblique sinus.  

==The morphologically left atrium==

'''A.'''  This view from the left-lateral aspect shows the finger-like left atrial appendage with the left atrium situated posteriorly. The left ventricle tapers to a rounded apex.  

<br>'''B.'''  This section through the aortic root and mitral valve displays the left atrial aspect of the septum enface. The crescentic edge (arrow) of the fossa valve has not sealed completely resulting in a PFO. The asterisk marks the location of the transverse pericardial sinus.]]

==The morphologically right ventricle==

'''A.''' The right ventricle is opened to show the septum and the muscular crest separating tricuspid from pulmonary valves. The moderator band (open arrow) extends from the foot of the septomarginal trabeculation to the free wall of the right ventricle. Coarse trabeculations fill the apical component.

<br>'''B.''' This close-up view of the tricuspid valve at the commissure between septal and antero-septal leaflets shows the annulus (broken line) crossing the membranous septum (dots) dividing it into atrioventricular(av) and interventricular(iv) components.]]

==The coronary circulation==

Diagram showing the right (RCA) and left (LCA) coronary arteries and their main ventricular branches. The left anterior descending (LAD) and posterior descending (PDA) coronary arteries mark the anterior and posterior margins of the ventricular septum.]]

==The cardiac conduction system==

The cardiac conduction system. Normally, the insulating fibro-fatty tissue plane at the atrioventricular junction prevents atrial myocardium from contacting ventricular myocardium. The penetrating bundle is the only muscular bridge.]]