The heart has two halves, a left and a right, each with two chambers - the atrium and the ventricle. Between the chambers are the heart valves which ensure the blood runs only in one direction. There are also heart valves situated between the ventricles and the major arteries - the aorta and pulmonary artery - where they have the same function. Failure in a valve in the left side of the heart - the aortic or the mitral valve - results in left-sided heart failure. This leads to an accumulation of fluids in the lungs, or pulmonary oedema. Valve diseases of the right side of the heart - the pulmonary and tricuspid valve - are rare but can occur as the result of some forms of congenital heart disease or long-term left-sided heart failure. Right-sided heart failure is characterised by fluid accumulation in the body, particularly in the legs, abdominal cavity and the liver. Malformation of the heart valves can be divided into two categories: narrowed (stenosed) valves and leaking (regurgitant) valves - or a combination of both. | 
