Webster's New World Medical Dictionary

heart transplant
An operation in which a dis-
eased or malfunctioning heart is replaced with a
healthy donor heart taken from a deceased person.
See also 
transplant.
heart valve
One of the four heart valves. All four
heart valves are one-way valves, permitting forward
and avoiding backward flow of blood. Blood enter-
ing the heart first passes through the tricuspid valve,
and then the pulmonary valve. After returning from
the lungs, the blood passes through the mitral
(bicuspid) valve and leaves the heart via the aortic
valve to pass through the aorta.
heart ventricle
One of the two lower chambers
of the heart. The right ventricle receives blood from
the right atrium and pumps it into the lungs via the
pulmonary artery, and the left ventricle receives
blood from the left atrium and pumps it into the cir-
culation system via the aorta.
heartburn
An uncomfortable feeling of burning
and warmth that occurs in waves, rising up behind
the breastbone (sternum) and moving toward the
neck. Heartburn has nothing to do with the heart. It
is usually due to gastroesophageal reflux, the return
of stomach acid into the esophagus. See also 
gas-
troesophageal reflux disease.
heart-lung machine
A machine that does the
work both of the heart and of the lungs: pumping
and oxygenating blood. Blood returning to the heart
is diverted through a heart-lung machine before
being returned to arterial circulation. Such
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heart-lung machine
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machines may be used during open-heart surgery.
Also known as pump-oxygenator or cardiopul-
monary bypass machine.