Are heart valve abnormalities classified as birth defects?

Some. A bicuspid aortic valve or a prolapsing mitral valve are present from birth. Many other heart valve abnormalities are acquired, either through scarring from infection, calcium deposition, or mal-apposition due to dilatation of cardiac chambers, among other things.
Yes. Children's heart valve abnormalities are classified as birth defects if the abnormalities were present at birth, which is the usual case. A person can get a heart valve defect later, such as due to infection or trauma.

Related Questions

Can someone survive with torn heart valve?

Usually no. Probably the most common "torn heart valve" is the mitral valve with a ruptured support structure. Frequently when a patient has a ruptured mitral valve apparatus, they are in dire need of mitral valve repair and do not do well in its absence. Rarely however, the patient will be ok for some time, but since mitral insufficiency can be asymptomatic until it's too late, i would not wait too long. Read more...
Sure... for a while. The issue is how torn, and how much leakage is coming along for the ride. In an ICU setting, we can usually keep things under control even when it's severe until we can do surgery. Less severe problems may not even need treatment (huge portions of the population have trivial amounts of leakage of one or more valves and this should not prompt concern). Read more...

How possible is it that I will need a new heart valve?

New heart valve. If your valves are normal then very low probability you'll need a new valve. If you have a seriously malfunctioning valve causing hemodynamic problems, you have a high probability of needing a new valve. Read more...