Normally the cardiac apex or apex beat is on the left
side. In the condition called dextrocardia, the apex
is on the right side (Fig. 18.9). Dextrocardia may be
part of a condition called situs inaersus in which all
thoracic and abdominal viscera are a mirror image
of normal.Bose of lhe Heorl
The base of the heart is also called its posterior surface.
It is formed mainly by the left atrium and by a small
part of the right atrium.
In relation to the base one can see the openings of
four pulmonary veins which open into the left atrium;
and of the superior and inferior venae cavae (Latin,
empty rsein) which open into the right atrium. It is related
to thoracic five to thoracic eight vertebrae in the lying
posture, and deicends by one vertebra in the erect
posture. It is separated from the vertebral column by
the pericardium, the right pulmonary veins, the
oesophagus and the aorla (see Figs 15.2 and 18.8).
Borders of the Heorl
L The upper border is slightly oblique, and is formed
by the two atria, chiefly the left atrium.
(^2) The rightborder is more or less vertical and is formed
by the right atrium. It extends from superior vena
cava to inferior vena cava (IVC).
3 The inferior border is nearly horizontal and is formed
mainly by the right ventricle. A small part of it near
the apex is formed by left ventricle. It extends from
IVC to apex.
PEBICARDIUM AND HEART
4 The left border is oblique and curved. It is formed
mainly by the left ventricle, and partly by the left
auricle. It separates the anterior and left surfaces of
the heart (Fig. 18.7). It extends from apex to left
auricle.
Surfoces of the Heorl
The anterior or sternocostal surface is formed mainly by
the right atrium and right ventricle, and partly by the
left ventricle and left auricle (Fig. 18.15). The left atrium
is not seen on the anterior surface as it is covered by
the aorta and pulmonary trunk. Most of the stemocostal
surface is covered by the lungs, but a part of it that
lies behind the cardiac notch of the left lung is
uncovered. The uncovered area is dull on percussion.
Clinically it is referred to as the area of superficial cardinc
dullness.
The inferior or diaphragmatic surface rests on the
central tendon of the diaphragm. It is formed in its left
two-thirds by the left ventricle, and in its right one-
third by the right ventricle. It is traversed by the
posterior interventricular groove, and is directed
downwards and slightly backwards (Fig. 18.8).
Theleft surface is formed mostly by the left ventricle,
and at the upper end by the left auricle. In its upper
part, the surface is crossed by the coronary sulcus. It is
related to the left phrenic nerve, the left peri-
cardiacophrenic vessels, and the pericardium.
Types of Circulolion
There are two main types of circulations, systemic and
pulmonary. Table 18.1 shows their comparison.
Dissection
Cut along the upper edge of the right auricle by an
incision f rom the anterior end of the superior vena caval
opening to the left side. Similarly cut along its lower
edge by an incision extending from the anterior end of
the inferior vena caval opening to the left side. lncise
the anterior wall of the right atrium near its left margin
and reflect the flap to the right (Fig. 18.10).
On its internal surface, see the vertical crista
terminalis and horizontal pectinate muscles.
The fossa ovalis is on the interatrial septum and the
opening of the coronary sinus is to the left of the inferior
vena caval opening.
Define the three cusps of tricuspid valve.Posilion
The right atrium is the right upper chamber of the heart.
It receives venous blood from the whole body, pumps