The inner layer, or
consists of epithelium and underlying connective tissue.
The endocardium also contains blood vessels and some
specialized cardiac muscle fibers called
described later in this chapter in the section entitled “Cardiac
The endocardium lines all of the heart chambers and
covers the structures, such as the heart valves, that pro-
ject into them. This inner lining is also continuous with the
inner linings (endothelium) of the blood vessels attached to
the heart and throughout the cardiovascular system.
summarizes the characteristics of the three layers of the
Heart Chambers and Valves
Internally the heart is divided into four hollow chambers,
two on the left and two on the right. The upper chambers,
), have thin walls and
receive blood returning to the heart. Small, earlike projec-
ri-klz) extend anteriorly from the
atria, slightly increasing atrial volume (see F
g. 15.4). The
lower chambers, the
tri-klz), force the blood
out of the heart into arteries.
A structure called the
right from the left atrium. An
the two ventricles. The atrium on each side communicates
with its corresponding ventricle through an opening called
u-lar ori-F s),
guarded by an
Grooves on the surface of the heart mark the divi-
sions between its chambers, and they also contain major
blood vessels that supply the heart tissues. The deepest of
ammation oF the pericardium due to viral or bacte-
rial inFection produces adhesions that attach the layers oF the pericar-
dium to each other. This condition is painFul and interFeres with heart
Where is the heart located?
Where would you listen to hear the apical heartbeat?
Distinguish between the visceral pericardium and the parietal
What is the Function oF the f
uid in the pericardial cavity?
Wall oF the Heart
The wall of the heart is composed of three distinct layers: an
outer epicardium, a middle myocardium, and an inner endo-
(f g. 15.5)
de-um), which corresponds
to the visceral pericardium, protects the heart by reducing
friction. It is a serous membrane that consists of connec-
tive tissue covered by epithelium, and it includes capillaries
and nerve F
bers. The deeper portion of the epicardium often
contains fat, particularly along the paths of coronary arteries
and cardiac veins that provide blood ﬂ ow through the myo-
The middle layer, or
is thick and largely consists of the cardiac muscle tissue that
pumps blood out of the heart chambers. The muscle F bers are
arranged in planes, separated by connective tissues richly sup-
plied with blood capillaries, lymph capillaries, and nerve F bers.
Base of heart
Apex of heart
The heart is posterior to the sternum, where it rests upon the diaphragm.