**1. Introduction**

All the vessels that drain blood out of the heart are called artery, and those that drain blood into the heart are called vein. Pulmonary veins, literally, are the vessels that transport oxygenated blood from the lungs back to the left atrium. The information of those veins is hardly found in veterinary textbooks. First of all, this chapter is focus on the development of those veins in fetus. If something wrongs during the process, different type of the abnormality leads to different results. The diagnosis, treatment and prognosis in human medicines are introduced simply in this chapter. In addition, pulmonary venous abnormalities in the veterinary medicines are reported in several species. Those case reports will also be briefly reviewed in this chapter.
