My brother, 53 yrs old, had an artificial valve placed after his dr found that he had an enlarged heart. This was in 1998. The last few months, he has had chest pains nearly every day. This wk, the dr told him he had two black spots on his heart & would need to see a heart specialist. He s also on coumadine. The family is very worried, of course. What could this be & is it life-threatening?