The inlet from the right atrium into the right ventricle is guarded by the right atrioventricular (tricuspid) valve. It has three cusps as its name implies. Each flap-like cusp is attached to the fibrous atrioventricular ring laterally.

Tough strands of fibrous tissue, the chordae tendinae, attached to the free edge of each cusp and to papillary muscles in the ventricular wall.

The papillary muscles contract when the ventricular walls contract, taking up slack in the chordae tendinae, thus preventing the eversion of the valve flaps when ventricular pressure exceeds that in the atrium, and thus preventing back flow into the atrium. The atrial sides of each cusp in contact with flowing blood are smooth whereas the ventricular sides are roughened by the insertion of the chordae tendinae.

The outlet from the right ventricle is into the pulmonary trunk guarded by the pulmonary valve. The valved comprises three semilunar cusps attached to the atrial wall at their bases. Each cusp is shaped like a pocket with a concave side facing into the pulmonary trunk. The cusps are pressed against the wall of the artery when the ventricle contracts and are filled with blood flowing back when pressure in the right ventricle falls below that in the pulmonary artery; they distend and thus occlude the pulmonary artery.

The semilunar cusps have great intrinsic strength because of their shape and require no external bracing.

The myocardium of the ventricles is thicker than that of the atria with numerous muscle bundles, the trabeculae carneae, forming irregular elevations on their internal surfaces. A muscular bundle, the moderator band, crosses the ventricle from septal to anterior wall, carrying the right branch of the atrioventricular bundle.