Answer: While it may make you uneasy to skip the antibiotic you've taken in the past to prevent an infection of your leaky heart valve, the latest guidelines from the American Heart Association and the American Dental Association support your new doctor.

The guidelines are based on the lack of evidence that taking antibiotics before dental procedures for most heart valve conditions reduces the risk of developing infective endocarditis. Folks' thickened hearts or valve problems are already exposed to bacteria from the mouth, which can enter their bloodstream during basic daily activities such as brushing or flossing.

The new guidelines are based on a number of studies that indicate that endocarditis is more likely to occur as a result of these everyday activities than from a dental procedure. Taking antibiotics unnecessarily can lead to antibiotic-resistant bacteria as well as side effects or allergic reactions.

There are still some heart conditions where antibiotics before dental work is still advised. This includes folks with artificial heart valves, and those with a history of infective endocarditis and certain serious heart valve conditions.

Thymus' importance wanes as we get older

A: In adults you won't find much thymus tissue, but its remnants can be found in the upper chest, extending from the base of the throat to the front of the heart. It consists of two flattened and elongated lobes.

During our development as a fetus and during our life before puberty, the thymus gland is involved in the production and maturation of lymphocytes, the white blood cells that protect us against viruses, fungus and other types of infections. These lymphocytes, called T cells, develop in the thymus and then travel to the various lymph nodes throughout our body.

While the thymus is critical to health in our early years, it seems to have much less importance as we get older. That's because the lymph nodes throughout our body are in place to help wall off the variety of infections that threaten to get into our bloodstream. The thymus gland weighs about a half-ounce at birth, reaching a maximum weight of about one ounce by puberty. After that, it slowly decreases in size, and thymus tissue is gradually replaced by fat and connective tissue.