Hi there my question for today is..how long do you have to have rheumatic fever before you find out you have it?

Rheumatic fever: Rheumatic fever is a syndrome that may follow after certain streptococcal infections including "strep throat." While the full-blown syndrome produces significant symptoms, some patients do not remember having this illness and yet later in life develop the valve complications of rheumatic heart disease.

Depends: It may be acutely that may present within days to weeks after the initial infection or may not present till years of having caused problems that were not picked up.