See also OPEN HEART SURGERY; RHEUMATIC HEART
DISEASE.
heart rate The number of times in a minute that
the HEARTcompletes a CARDIAC CYCLE, commonly
measured as the PULSE. At rest, the healthy adult
heart beats between 60 and 80 times per minute.
The heart rate of a person who is aerobically fit is
slower because the heart is more efficient and can
pump more blood with each contraction. CARDIO-
VASCULAR DISEASE(CVD) that reduces CARDIAC CAPAC-
ITYoften results in an increased heart rate as the
heart attempts to compensate for decrease in vol-
ume per beat. An unusually rapid heart rate at
rest is tachycardia; an unusually slow heart rate at
rest is bradycardia. Noncardiac health conditions
also can affect heart rate. Heart rate may increase
with HYPERTHYROIDISMand decrease with HYPOTHY-
ROIDISM. Other factors that increase heart rate
include physical activity, stress, fear, and FEVER.
An aerobically fit heart can increase its pumping
volume at a lower increase in heart rate to meet the
body’s oxygen needs during physical activity or
exercise. The heart’s maximum heart rate is the
upper limit of cardiac function and declines with
increasing age. Health experts recommend physical
activity for aerobic conditioning that puts the heart
rate between 25 and 75 percent of maximum heart
rate for 20 to 30 minutes. An individual’s target
heart rate varies according to AEROBIC FITNESSlevel.
The most effective method for reaching and staying
within the target heart rate during exercise is to use
a heart monitor, which counts the heartbeats of the
person wearing it.
See also AEROBIC EXERCISE; AEROBIC FITNESS;
ARRHYTHMIA; EXERCISE AND HEALTH; FITNESS LEVEL;
PHYSICAL EXERCISE AND CARDIOVASCULAR HEALTH;
WALKING FOR FITNESS.
heart sounds The sounds of the opening and
closing of the heart’s valves and the passage of
BLOODthrough them. HEARTsounds are an impor-
tant component of physical diagnosis for cardio-
vascular conditions. Doctors listen to them using a
STETHOSCOPE.
The classic lubb duppsounds are the normal
heart sounds in a healthy adult. These are the first
and second heart sounds, designated S1 and S2.
S1 represents the closing of the tricuspid and
mitral valves between the atria and the ventricles.
S2 represents the closing of the pulmonary and
aortic valves as blood leaves the right and left ven-
tricles, respectively. Other heart sounds are abnor-
mal in adults, occurring only with certain health
(and usually heart) conditions. They include- S3, sometimes called a pericardial knock, indi-
cates a dilated ventricle and ventricular dysfunc-
tion such as may occur with CARDIOMYOPATHY
(though S3 may be a normal heart sound in
young children) or HEART FAILURE. S3 is a low-
pitched, vibrational sound the doctor can hear
using the bell of the stethoscope. - S4, indicates abnormal MUSCLE tissue in the
heart such as might occur with MYOCARDIAL
INFARCTIONor hypertrophic cardiomyopathy. S4
also may occur with ISCHEMIC HEART DISEASE
(IHD) and HYPERTENSION. Like S3, S4 is a low-
pitched vibration the doctor hears with the bell
of the stethoscope. - A click is a high-pitched tone following S1 that
indicates improper closing of a valve such as
might occur with AORTIC STENOSISor pulmonary
artery stenosis, particularly when these condi-
tions are congenital. - A snap is a sharp sound following S2 that is
typical with mitral stenosis. - A murmur is a whooshing or whispering sort of
sound that indicates blood flowing back
through an incompletely closed valve. The tim-
ing and quality of the murmur’s sound help
determine which valve is dysfunctional. Heart
murmurs are common and often have no car-
diovascular significance, though persistent
murmurs may indicate VALVULAR HEART DISEASE.
The cardiologist may choose to further investi-
gate persistent abnormal heart sounds using ELEC-
TROCARDIOGRAM(ECG), ECHOCARDIOGRAM, and other
diagnostic procedures depending on the person’s
symptoms and cardiovascular history.
See also AUSCULTATION; CONGENITAL HEART DISEASE;
HEART MURMUR.heart transplantation The replacement of a dis-
eased HEARTwith a healthy heart from a deceased
donor. Heart transplantation is a therapeutic60 The Cardiovascular System