Artificial heart valve Artificial heart valve An artificial heart valve is a device implanted in the heart of a patient with valvular heart disease. When one of the four heart valves malfunctions, the medical choice may be to replace the natural valve with an artificial valve. This requires open-heart surgery. Valves are integral to the normal physiological functioning of the human heart. Natural heart valves are evolved to forms that perform the functional requirement of inducing unidirectional blood flow through the valve structure from one chamber of the heart to another. Natural heart valves become dysfunctional for a variety of pathological causes. Some
MD Helicopters MD 500 in 1953. Images and analyses done regarding North Korea's MD 500 helicopters show that they have been modified significantly to serve as light attack helicopters, such as modification work on the helicopters for them to be mounted with Soviet-designed AT-3 Sagger anti-tank wire-guided missiles. The MD 500 is widely operated by private individuals, companies and law enforcement agencies around the world. MD Helicopters MD 500 The MD Helicopters MD 500 series is an American family of light utility civilian and military helicopters. The MD 500 was developed from the Hughes 500, a civilian version of the US Army's OH-6A Cayuse/Loach.