1. The heart. The heart is a muscular organ that pumps blood throughout the body. It is essential for life, and without it, the body would not be able to function.

2. The diaphragm. The diaphragm is a large muscle that separates the chest cavity from the abdominal cavity. It is responsible for breathing, and it also helps to maintain abdominal pressure.

3. The skeletal muscles. The skeletal muscles are the muscles that are attached to the bones. They are responsible for movement, and they also help to maintain posture.