You don't feel afraid because your heart races — both happen at once, independently
Walter Cannon and Philip Bard challenged the idea that physical arousal causes emotion, arguing instead that a feared stimulus triggers the feeling of fear and the racing heart in parallel, through separate brain pathways, rather than one causing the other. They pointed out that the same bodily state, like a pounding heart, shows up in wildly different emotions, so the body alone can't be what tells you which one you're having.