ACE2, or Angiotensin-Converting Enzyme 2, is a protein found on the surface of many cells in the human body, particularly in the lungs, heart, and kidneys. It plays a crucial role in regulating blood pressure and maintaining fluid balance by converting angiotensin II, a hormone that constricts blood vessels, into a molecule that dilates them. This helps to lower blood pressure and protect the cardiovascular system. In the context of COVID-19, ACE2 gained attention as the entry point for the SARS-CoV-2 virus, which causes the disease. The virus's spike protein binds to ACE2, allowing it to enter and infect human cells. Understanding ACE2's function is essential for developing treatments and vaccines against COVID-19.