Galen and William Harvey were the ones who made great contributions to the discovery of medicine .In around 162 AD Galen laid the foundation of circulatory system through his experiments on dead people and animals since he was not allowed access to human bodies. He believed that the liver produced blood and was pumped by veins to the rest of the body in an open ended system. He also believed that the heart was a source of innate heat which was cooled off by respiration which provided vital spirits. Galen managed to demonstrate that arteries carry out both blood and air in contrast to another theory before him which stated that they contain air only. He also discovered that the heart and arteries intrinsically pulsate and that arteries and veins carry the same blood.

Many years after Galen his work continued to be used until, Harvey later revolutionized the cardiovascular system. He carried out experiments on humans and proposed that the heart pumps blood and it circulated in a closed system through both veins and arteries. He also discovered that arterial pulse is due impulses of blood from the left ventricle. He also demonstrated that blood enters the limbs via arteries and leaves through veins and that venous valves promote centripetal flow of blood from the smaller veins to greater veins.

Both Galen and Harvey's work greatly impacted medical practice ,scientific inquiry and our understanding of the cardiovascular system. Galen's theories helped medical practices in the early centuries before Harvey even after he had died since his theories were more accurate than the ones postulated before him which suggested that arteries are filled with air from the heart. His theory which suggested that the heart was the innate source of heat was only ruled out after the discovery of thermometer which was many centuries later .Galen also made a very big impact to the practice of medicine as he paved the way for Harvey who based most of his theories and experiments on Galen's work. Harvey discovered how the heart is the pump in a closed system and hence he greatly impacted medicine as up to this day researchers are still building their knowledge upon the foundation that they laid. This allows advancement in medical practice and scientific inquiry which allow us up to this day to make diagnosis on certain cardiovascular diseases like heart failure which are only understood after you have a clear understanding of how the heart normally works.

The theories by Galen and Harvey help us to know and appreciate the way how medicine is advancing and how much effort others ,many centuries ago dedicated their time to discovering things that are helping us up to this day. It also encourages us to even research more since they already demonstrated that what you discover today can bring about better medical practice and your legacy will continue many years after your death.