What is infective endocarditis? Does infective mean it's contagious?

Bacteria. Infective endocarditis is a bacterial blood infection that has infected the heart as well. It is not contagious.
Endocarditis. Even though it is called infective endocarditis, it is not a contagious disease the way some other diseases are e.g. Hicken pox is. The name implies that it is an infectious process that involves the structures of the heart (valves, the covering of the heart, and sometimes the muscles of the heart).
Heart infection. Usually bacterial (rarely fungal) this infection affects the valves in the heart by causing an active infection damaging the valves. In normal people this is rare, but those with congenital abnormalities of the valves or heart are more susceptible. Iv drug use can also increase the chances of this infection. It can be acute which is very serious, or subacute which tends to be harder to detect.