The live model can be made from different materials but the most preferred one would be with clay.
Take some clay (non-toxic ones) and make it in a shape of a irregular triangle with the end just a bit pointer.
Now you can use some thick tubes (pipes etc) cut it into pieces and make the pulmonary artery & the pulmonary vein (which carries the blood away & into the blood). Stick these structures of pipes to the clay model with help of adhesive, tapes etc.
Now colour the clay model of the heart, make thin structures with red&blue paint (red will be for oxygenated blood & blue will be for deoxygenated one) along with pipes of red & blue..
So, there your live model of HEART is ready..
Hope it helped you..
A picture attached will help you further..