Pulmonary trunk
A vessel that arises from the right ventricle of the heart, extends upward, and divides into the right and left pulmonary arteries that convey unaerated blood to the lungs.
When the right ventricle contacts, the blood inside it is put under pressure and the tricuspid valve between the right atrium and ventricle closes.
The only exit for blood from the right ventricle is then through the pulmonary trunk.
The pulmonary trunk is to the right ventricle what the aorta is to the left ventricle -- the outlet vessel