Currently, people's heart rates default to 60 whether it's smooth sailing or 8 Hammerheads are attacking.
In GetHeartrate after defining `float rate = NormalHeartrate;`, adding the line

rate *= 1.0f + (GameMain.GameSession?.EventManager != null ? GameMain.GameSession.EventManager.MusicIntensity * 2.0f : 0.0f);

will make the heart rate scale from 60 - 180 depending on current intensity (as far as I can find, that's about normal for healthy 30 - 40 year old people). That way people will at least seem excited (or scared) if there's a lot going on.