The words: "сердцебиение" and "долгосрочно" are compound words (they are composed of two component words each).
I have the impression that the first "e" is still pronounces as "e" in the word сердцебиение and the first "o" as an "o" in the word долгосрочно.
Question: In compound words the stress of the two component word remains? Or differently does compound words have two stresses?