The structure indicated is the pulmonary valve.
There are four sets of valves in the heart. Between the atria and the ventricles are the atrioventricular valves; on the right is the tricuspid valve, on the left is the mitral (bicuspid) valve.
Between the ventricles and the aorta/pulmonary trunk are the semilunar valves. The pulmonary valve is located between the right ventricle and the pulmonary trunk, and the aortic valve is located between the left ventricle and the aorta.
The pulmonary valve (pulmonic valve) has three cusps. The pulmonary valve opens in ventricular systole, when the pressure in the right ventricle becomes greater than the pressure in the pulmonary trunk, thereby forcing the valve open. At the end of ventricular systole, the pressure in the right ventricle falls, and the pressure in the pulmonary trunk is greater, thereby forcing the closure of the pulmonary valve.
The three cusps of the pulmonary valve are:
- Left cusp
- Right cusp
- Anterior cusp
The free superior edge of these cusps thickens in the middle to form a nodule, laterally it is thinner and is called the lunule.
Learn more about the anatomy of the heart in these tutorials: