<s>
A	O
premature	B-Algorithm
heart	I-Algorithm
beat	I-Algorithm
or	O
extrasystole	B-Algorithm
is	O
a	O
heart	O
rhythm	O
disorder	O
corresponding	O
to	O
a	O
premature	O
contraction	O
of	O
one	O
of	O
the	O
chambers	O
of	O
the	O
heart	O
.	O
</s>
<s>
Premature	B-Algorithm
heart	I-Algorithm
beats	I-Algorithm
come	O
in	O
two	O
different	O
types	O
:	O
premature	B-Algorithm
atrial	I-Algorithm
contractions	I-Algorithm
and	O
premature	B-Error_Name
ventricular	I-Error_Name
contractions	I-Error_Name
.	O
</s>
<s>
Often	O
they	O
cause	O
no	O
symptoms	O
but	O
may	O
present	O
with	O
fluttering	O
in	O
the	O
chest	O
or	O
a	O
skipped	B-Algorithm
beat	I-Algorithm
.	O
</s>
<s>
They	O
are	O
the	O
most	O
common	O
arrhythmia	B-Application
.	O
</s>
<s>
Premature	B-Algorithm
heart	I-Algorithm
beats	I-Algorithm
can	O
be	O
asymptomatic	O
(	O
the	O
patient	O
does	O
not	O
complain	O
about	O
anything	O
)	O
.	O
</s>
<s>
The	O
subject	O
may	O
experience	O
palpitations	B-Algorithm
,	O
a	O
feeling	O
of	O
cardiac	O
"	O
pause	O
"	O
.	O
</s>
<s>
Electrocardiography	B-Application
and	O
laser	O
Doppler	O
imaging	O
allow	O
to	O
visualize	O
Premature	B-Algorithm
heart	I-Algorithm
beats	I-Algorithm
.	O
</s>
