I've tried to break down each word and particle to decipher the meaning myself since I think that'd be the best way to fully grasp it. So far I've got it down to "I stop because the voice of my heart is crying."
I know that 誰 usually means who but is more commonly used to refer to a person rather than a direct translation to who, though I couldn't find something to back up that it could refer to ones self.
Right after that it says “が止める” which I figure should stay right after "I" rather than going at the end of the sentence referring to how he could stop the heart from crying.
“というの” I did research on this one since it did confuse me quite a tad, I found that it's most commonly used as "someone says A" or "I heard that A". The translations I've found the most are "means", "that is to say", or "because"; since he is referring to himself I figure the の gives it a somewhat possessive tone, though if it doesn't I still believe it would be "because" in the end due to the 誰 at the beginning.
“叫んだ” I've found could be a colloquial inflection of “さけんぶ” where as the だ replaces ぶ, it's still a particle meaning "is".
Now “声を” being at the end kind of confuses me a little, as the を is indeed referring to the subject at hand, why is at the end and not before sakenda, or even before kokoro? Does the placement have a specific effect or is that just more grammatically correct?