surgery (i.e. coronary artery bypass surgery) should also have their valve addressed by the surgical team if echocardiography unveils significant heart problems. Low gradient aortic stenosis with concomitant left ventricular dysfunction poses a significant question to the anesthesiologist and the patient. Stress echocardiography (i.e. with dobutamine infusion) can help determine if the ventricle is dysfunctional because of aortic stenosis, or because the myocardium lost its ability to contract. Aortic insufficiency Many people with aortic insufficiency often do not develop symptoms until they have had the condition for many years. Aortic valve replacement is indicated for symptoms such as shortness of breath, and in cases where the heart has begun to enlarge (dilate) from pumping the increased volume of blood that leaks back through the valve. Types of valves There are two basic types of replacement heart valve: tissue (bioprosthetic) valves and mechanical valves. Tissue valves Tissue heart valves are usually made from animal tissue (heterografts) mounted on a metal or polymer support. Bovine (cow) tissue is most commonly used, but some are made from porcine (pig) tissue. The tissue is treated to prevent rejection and calcification (where calcium builds up on the replacement valve and stops it working properly). Occasionally, alternatives to animal tissue valves are used: aortic homografts and pulmonary autografts. An aortic homograft is an aortic valve from a human donor, retrieved either after their death or from their heart if they are undergoing a heart transplant. A pulmonary autograft, also known as the Ross procedure is where the aortic valve is removed and replaced with the patient's own pulmonary valve (the valve between the right ventricle and the pulmonary artery). A pulmonary homograft (a pulmonary valve taken from a cadaver) is then used to replace the patient's own pulmonary valve. This procedure was first performed in 1967 and is used primarily in children, as it allows the patient's own pulmonary valve (now in the aortic position) to grow with the child. Tissue valves can last 10–20 years. However, they tend to deteriorate more quickly in younger patients. New ways of preserving the tissue for longer are being investigated. One such preservation treatment is now being used in a commercially available tissue heart valve. In sheep and rabbit studies, the tissue (called RESILIA tissue) had less calcification than control tissue. However, long-term durability data in patients are not yet available. Stented and stentless tissue valves are available. Stented