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 Explorer MD Helicopters MD Explorer The MD Helicopters MD Explorer is a light twin utility helicopter. Designed in the early 1990s by McDonnell Douglas Helicopter Systems, it is currently produced by MD Helicopters. There have been two models, the original MD 900, and its successor, the MD 902. In January 1989, McDonnell Douglas Helicopters officially launched the development of the Explorer, initially referred to as MDX. The Explorer was the first McDonnell Douglas helicopter to incorporate the NOTAR system from its initial design. McDonnell Douglas partnered with Hawker de Havilland of Australia to manufacture the airframes. 10 prototypes were built with