Looking at (dissecting) hearts in primary
schools
The term “dissection” is used in this and the other primary documents to mean just close
observation. The cutting into the organ does not require special equipment or skills.
Why do this?
The dissection can help pupils to work out how blood flows through the heart.
It also gives pupils an opportunity to design and carry out methods for working out the blood flow
and measuring the volumes of internal cavities.
Where to obtain the hearts
Hearts obtained from a butcher or shop that sells for human consumption will have hearts that
are suitable. A pluck will also often contain a heart. See “Looking at (dissecting) plucks in primary
schools”.
Safety
Please refer to the safety guidelines are in CLEAPSS guide, “Looking at (dissecting) animal
organs in primary schools, health and safety aspects”.
Carrying out the dissection
External examination
Examine the heart, noting the muscle(red)
and fat (white). Explain that the size of the
lamb’s heart is about the same as an adult
human’s.
Each pupil’s heart will be about the same
size as their fist.
Show the blood vessels on the outside of
the heart that supply the heart muscle.
Explain that when a person has a heart
attack, the blood vessels become blocked.
Explain that any cuts in the heart are made
when it is cut from the animal’s body.
Blood
vessel
Finding the blood vessels that carry blood to and from the
heart
Show the pupils the top of the
heart.
Only some blood vessels will
be present as the
butcher/abattoir often slices
the top of the heart away.
The pupils can put their
fingers into the blood vessels
to fee the cavity inside the
heart.
HEALTH and SAFETY
Make sure that pupils wash
their hands immediately after
handling the heart.
Working out the blood flow through the heart
The pupils can suggest a
vessel they think might carry
blood into the heart.
They can place a flag made by
attaching a “Post-it” to a
cocktail stick onto the “IN”
vessel.
Pupils then pour water into their
“IN” vessel, and see where it
comes out.
Sometimes you can use a funnel
(as shown here).
Sometimes it is best to pour into
the heart (as shown here).
It is easier to see the water flowing
out if a little food colouring is
added (green has been added in
this case)
If water is poured into an “OUT”
vessel, the valves may stop the
flow so no water flows through the
heart.
Coloured water
flowing out
Pupils label the outflow vessel as
“Out”.
The process is then repeated for
the other two blood vessels
Cutting into the heart
Use kitchen scissors to make a
horizontal cut across the top of
the heart
The cut surface will show the
cavities that fill up when the
blood enters the heart.
One of these entry chambers is
called an atrium.
atrium
Make a 2nd cut further down the
heart and you can see the
chambers where blood collects
before it is pumped out of the
heart. Each of these chambers
is called a ventricle.
ventricle
You might also be able to see
the valves that separate the
atrium from the ventricle.
The muscle wall of the heart is
also very clear.
muscle
valve
The pupils could suggest ideas for why there is more muscle around one of the ventricles.
Measuring the volume of the ventricles
Measure some water into a
measuring cylinder of jug, and
carefully pour it into the
ventricle.
Sop when the ventricle is full
See how much water has been
used.
We had 50ml in the measuring
cylinder before we started filling
the ventricle.
The pupils can speculate about the volume of the other ventricle, then measure it.
Opening up the ventricles
Please refer to the safety guidelines are in CLEAPSS guide, “Looking at (dissecting) animal
organs in primary schools, health and safety aspects”.
The opened ventricles show the
valves very clearly.
The valves stop the backflow of blood.
valve
Clearing away and disposal
Please refer to the safety guidelines are in CLEAPSS guide, “Looking at (dissecting) animal
organs in primary schools, health and safety aspects”.