• Presents at its apex a small conical auricular appendage
• Receives the superior and inferior vena cavae
• The sulcus terminalis extends between the two veins.

The interior of the right atrium shows several distinctive features:

• The posterior part is smooth walled (sinus venarum).
• The anterior part is rough with fine muscular ridges called musculi pectinati .
• Between these two parts is a definite ridge called the crista terminalis.
• It receives the following:
  a) The SVC
  b) IVC open into the smooth part.
  c) coronary sinus.
• The septal wall is oblique, has depression called fossa ovalis.
• The edge is known as limbus fossae ovalis .
• The posterior (non-coronary) aortic sinus abuts the upper part of the interactrial septum, and creates a bulge called torus aorticus.

Several of the internal features of the right ventricle are important.

• Between the tricuspic and pulmonary valves, the wall presents a thick muscular ridge called the supra ventricular crest.
  
  
• Below the crest, the wall is marked by massive irregular muscular ridges called trabeculae carneae. Three types of trabeculae are described:
  
  
• Ridges on the ventricular wall
  
  
• Those with free central parts, like bucket handles. One of these “ bucket handles ” trabeculae is particularly large and is known as the septomarginal trabecular or the moderator band . It extends from the septal wall to the base of the anterior papillary muscle, and contains part of the conducting system of the right bundle branch.
  
  
• Papillary muscles. These form comical projections from the ventricular and septal walls. Chordae tendineae attach to their sides and apices, and fan towards the tricuspid valve leaves.
  
  
• The outflow tract of the right ventricle, above the supra ventricular crest, is smooth-walled and is called the infundibulum or conus arteriosus.

The walls of the left atrium are thicker than those of the right atrium.

It has a small auricular appendage, which covers the origin of the left coronary artery and abuts the left side of the pulmonary trunk.

The Interior has few features of note:

• Musculi pectinate are limited to the auricular appendage. The rest of the cavity is smooth walled, reflecting a development from the foetal pulmonary veins.
  
  
• A depression can often be found on the interactrial wall corresponding to the site of ostium secundum of the fetal heart.
  
• The inflow channels are four pulmonary veins, two on each side, but the two veins on the left may enter the cacity by a single opening.

The Left Ventricle

Wall thickness 8-12 mm

Interventricular septum bulges to the right

Internal features:

• The wall is ridged by trabeculae carneae
  
  
• Close to the aortic orifice, there is a round area of interventricular septum which is membranous in nature. Its fibres are continuous with the fibious supports for the cusps of the aortic valve.
  
  
• Two papillary muscles in the left ventricle, an anterior and a posterior muscle.
  
  
• The types of chordae found in the left ventricle present similar features to those of the right chamber.

Two rough zone chordae, however, are particularly thick in the left ventricle, and are called strut chordae. They arise from the tips of the anterior and posterior papillary muscles, and insert into the anterior leaflet of mitral valve.