Smallest cardiac veins contribute to normal physiologic shunting of blood. As a consequence of the input of these vessels, blood in the left heart is less oxygenated than the blood found at the pulmonary capillary beds, albeit to a very small degree. The "openings of smallest cardiac veins" are located in the endocardium. Here the smallest cardiac veins return blood into the heart chambers from the capillary bed in the muscular cardiac wall, enabling a form of collateral circulation unique to the heart. Not every endocardial opening connects to the thebesian veins as some connect to the vessels of Wearn, which are arteries.
Endometrial arteries blood to the endometrium but are also beneficial during pregnancy. When a female is pregnant a placenta develops. The baby receives blood, nutrients and oxygen via the umbilical cord which is attached to the placenta. Between the placenta and the myometrium are intervillous spaces where the endometrial arteries supply blood to. The placenta has villous trees which allow for blood to circulate and then be transported to the baby via the placenta. Endometrial arteries are divided into the common ones and the arteriovenous anastomosis. The common ones are arteries that are homologous to the arteries of the rest of the