My heart races out of no where? ?

im joinin the dance team but i had to get a physical and they didnt p me, becuz out of no were my heart will start racing and i feel dizzy all the time, i had a heart murmur wen i was little i dnt no if that has anything to dk with it but i have to go get a cardiac exam or something like that they said a 17 year old girl should not be going through this or having chest pains, plus i have a breathing problem which they said mite be ashythma but idk im kinda scardd?..