Two primary types ofcardiac muscle cellsare:

• Myocardial contractile cells
• Myocardial conducting cells

Figure 1.Cardiac muscle cells

Contractile cellsconstitute the bulk (99%) of the cells in the atria and ventricles. Contractile cells conduct impulse and are responsible for contractions that pump blood through the body.

Conducting cells(1%) form the conduction system of the heart. Their function is similar in many respect to neurons, although they are specialized muscle cells. Conduction cells initiate and propagate the action potential (electrical impulse) that travels throughout the heart and triggers the contractions that propel the blood.

Together withpacemaker cells, the myocardial contractile and conducting cells comprise the muscle tissue of the heart (myocardium).