That was actually a really fascinating talk I went to recently - the author's premise is that we have the same physical responses to strong emotions - pretty much ANY strong emotions. Your heart races, your palms get sweaty, you blush, you feel like you can't breathe, etc. That applies equally well to being afraid, nervous, in love, really angry, frustrated, etc. So as an author, you can't take a shortcut like "his heart raced" unless it's really obvious what the emotion is supposed to be. Also, since there are only so many autonomic nervous responses, almost all of them have cliched phrases ("she could feel her cheeks turn red," "her breath tangled in her throat," "his heart felt ready to leap out of his chest," etc.) and a good author will find ways to tweak those cliches so they don't sound cliched anymore.