1
.
The
shape
of
the
heart
is
similar
to
a
____________________
.
2
.
The
walls
of
the
heart
are
fairly
thick
,
approximately
like
a
____________________
____________________
____________________
,
at
the
bottom
.
On
the
top
,
they
?
re
thinner
,
about
as
thin
as
____________________
____________________
____________________
.
3
.
The
strips
of
muscle
at
the
bottom
of
the
heart
are
like
____________________
____________________
____________________
____________________
____________________
.
4
.
The
heart
is
so
small
.
It
?
s
only
slightly
larger
than
a
tightly
closed
____________________
.
5
.
That
?
s
the
heartbeat
.
Contraction
and
relaxation
?
very
regular
and
even
?
the
beat
is
just
like
the
____________________
____________________
____________________
____________________
____________________
.
6
.
The
heart
is
similar
to
a
____________________
.
Basically
,
it
pumps
blood
to
the
rest
of
the
body
