Making a model heart, whether for an art project or for a science class, can require some patience. Forming the shape of the heart also requires some dexterity. If you want to make the heart life-sized, model the heart to be about the size of your fist.
Shred the newspaper into pieces about 1 inch wide and at least 2 inches long. Enough paper to layer your heart more than once will be needed.
Shred the computer paper to the same size pieces. The computer paper will be used as your heart's outer layer, which will make painting the heart easier.
Put 4 cups of water into a pot on the stove and bring it to a boil. Once boiling, remove it from the stove.
Mix 1 room-temperature cup of water with 1 cup of flour, then pour this mixture into the hot water and mix well with a spoon. Add a dash of salt to the mixture to prevent mold from later growing on your paper mache.
Constructing the heart
Take a dowel rod and either glue it to the bottom of a shoebox or put it through a flat piece of styrofoam. Take some aluminum foil and wrap it loosely around the dowel. Gently crunch the foil around the dowel to make the shape of a heart.
Add as much foil as needed to make the core size of the heart. Take a piece of shredded newspaper and dip it in your paper mache mixture. Use your thumb and index finger to remove any clumps of the mixture; it just needs a light coat.
Begin to apply one layer of newspaper around the heart shape until the foil is completely covered. Allow this layer to dry overnight.
Then apply another layer of newspaper on top of the first layer. Let the second layer dry overnight. Once the second layer has dried, apply only one layer of computer paper on top of the entire heart and allow it to dry overnight.
Prime the heart for paint by adding a coating of acrylic primer over it. The primer should be sufficiently dry (a few hours) before you start painting.
Refer to Grey's Anatomy or the Powerhouse Museum websites, included in the resources listed below, as guides to painting your heart. Grey's Anatomy and Powerhouse Museum both provide detailed images for the location of veins and arteries on the heart.
The paper-mache paste should have the consistency of glue. If it's too thick or too watery, add more water or flour, respectively, until it's balanced.
Don't touch your heart model once you've applied paint. This will leave noticeable fingerprints.