What are the hearts muscles?

Atria:

- Receiving chambers.

- Thin walls.

- Auricles: ear-shaped appendages.

Ventricles:

- Pumping chambers.

- Thick walls.

- Papillary muscles: projections from ventricular wall.

- Chordae tendineae: white, fibrous cords.

- Trabeculae carneae: ridges of the myocardium.