Ibn NafisIbn Nafis (d. 1288) was the first person to accurately describe the process of blood circulation in the human body. Contemporary drawings of this process have survived.
In 1628 this was again 'discovered' by William Harvey. It was not uncommon for early Muslim medicine to be re-invented in Western Europe, or for ambitious Europeans to discover Muslim ideas and publish them as their own. It was also not uncommon for Europeans to simply not know of, or to disbelieve, Muslim discoveries, despite the fact that Rhazes, Avicenna, Al-Zahra and Al-Ibadi were well known.
This particular theory contradicted one of Galen, as Harvey discovered, to his chagrin. It may have been suppressed in Europe because it was a clear case where Muslim discoveries had contradicted classical discoveries, which Europeans sought to elevate as "their own".