There are three types of muscle in mammals. They are skeletal, smooth, and cardiac muscles. Skeletal muscles are found on those that are literally attached to the skeleton such as those found on your arms and legs. They can be controlled voluntarily. Cardiac muscles are found in the walls of the heart and move on an involuntary basis.
Finally, smooth muscles are found in hollow organs such as your stomach and esophagus and are also able to be controlled only on an involuntary basis. These are not found in your heart. Intercalated discs are found in the heart muscles and again, these have only involuntary movements.