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 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. The series currently includes the MD 500E, MD 520N, and MD 530F. The successful Hughes 500/MD 500 series began life in response to a U.S. Army requirement for a Light Observation Helicopter (LOH). Hughes' Model 369 won the contest against competition from Bell and Hiller. The subsequent OH-6 Cayuse first flew in February 1963. The 500 series design features shock-absorbing landing