The Human Heart
The heart is a hollow, cone-shaped muscle located between the lungs and behind the sternum (breastbone). Two-thirds of the heart is located to the left of the midline of the body and 1/3 is to the right (see Figure 1).
Figure 1
[Please note - Medical illustrations assume that the patient is
facing you so that the right and left correspond to the patient's
right and left. That's why the left and right labels here seem backwards.]
Heart Sounds When
someone listens to your heart with a stethoscope the sound is often
described as lub-dub lub-dub. The first heart sound (lub) is caused by
the acceleration and deceleration of blood and a vibration of the heart
at the time of the closure of the tricuspid and mitral valves. The
second heart sound (dub) is caused by the same acceleration and
deceleration of blood and vibrations at the time of closure of the
pulmonic and aortic valves. |
The apex (pointed end) points down and to the left. It is 5 inches (12 cm) long, 3.5 inches (8-9 cm) wide and 2.5 inches (6 cm) from front to back, and is roughly the size of your fist. The average weight of a female human heart is 9 ounces and a male's heart is 10.5 ounces. The heart comprises less than 0.5 percent of the total body weight.
The heart has three layers. The smooth, inside lining of the heart is called the endocardium. The middle layer of heart muscle is called the myocardium. It is surrounded by a fluid filled sac call the pericardium.
