The foramen of Panizza (named for anatomist Bartolomeo Panizza[1]) is a hole that connects the left and right aorta as they leave the heart of all animals of the order Crocodilia.
Two vessels, the left aorta and the pulmonary artery, exit the right ventricle.
Blood from the right ventricle goes to the lungs through the pulmonary artery, as in mammals and birds.
However, when a unique active valve leading to the pulmonary artery contracts, pressure in the right ventricle can increase, and blood can leave the right ventricle, enter the left aortic arch, and therefore bypass the pulmonary circulation.
However, some species of crocodilians have regulatory sphincters that prevent unwanted flow of blood through the foramen of Panizza during non-diving.