The statement is somewhat misleading. Pectinate muscles are actually found in the right atrium and the left atrium of the heart, not in the ventricles. These muscles are ridged bundles of muscle tissue that give the atrial walls a rough texture. They help in the contraction of the atria and assist in the movement of blood into the ventricles.
In contrast, the ventricles, particularly the right and left ventricles, contain structures known as trabeculae carneae, which are different from pectinate muscles. Trabeculae carneae are the irregular muscular ridges on the inner surfaces of the ventricles, helping to increase the surface area for contraction and prevent suction during the contraction phase.
To summarize, the atria contain pectinate muscles, while the ventricles feature trabeculae carneae, so the correct terminology would specify that pectinate muscles are found in the atrial chambers.