The "pulse" is produced by a 
pressure wave in the arterial
system as a result of the contraction of the left ventricle. This
wave may be felt in most 
major arteries although the most
commonly used vessels are the radial arteries and the carotids
arteries. Other convenient sites include the temporal, femoral,
posterior tibial and dorsal pedal arteries.
The radial pulse is measured by positioning the patient's hand palm up and placing two fingers against the radial artery located on the thumb side, just above the wrist. The radial pulse, because of its further distance from the heart, follows systole by 0.1-0.2 seconds.
The carotid pulse may be located on either side of the neck, just anterior to the sternomastoid muscle and lateral to the trachea. When auscultating the heart, it is wise to palpate the carotid pulse at the same time. Because of its position close to the heart it can be used to help identify heart sounds.
When palpating the pulse, the rate, rhythm, character and
volume of the pulse wave should be noted along with the character
of the vessel wall. The average 
pulse rate for a resting adult is
60-90 beats per minute. It fluctuates with activity, excitement,
eating, sleeping and many other normal functions. A resting pulse
rate of 45 is common in those who exercise regularly. Children's
pulse rates can vary normally from 90-140. In the young, the
pulse rate accelerates slightly during inspiration and slows
during expiration.
Most febrile diseases, anemia, hyperthyroidism and some
cardiac problems produce an elevated pulse rate. 
Paroxysmal
Atrial Tachycardia (PAT) (also called atrial tachycardia,
atrial
tachycardia with block, multifocal atrial tachycardia or
paroxysmal supraventricular tachycardia) is produced by a
"run-away" ectopic pacemaker and may sometimes be felt in the
pulse as very rapid, weak pulse waves.
Bradycardia may occur in patients with disturbed cardiac conduction systems (heart blocks). The ventricle may contract so inefficiently at times that a pulse is not detected even though a weak ventricular contraction may have occurred. This can take place on a regular basis between normal pulse waves or irregularly. At times the "dropped beats" may progress to the degree that cerebral artery perfusion is unsatisfactory and the patient loses consciousness (Adams-Stokes Syndrome).