According to the thread title - what makes you think he has bradycardia? Bradycardia is when the heart rate is less than 60bpm. Have you/him/the doc measured it and seen what it's at? When does he actually feel it slow down? If he feels it slow down as he breathes out, that's considered normal (related to the Bainbridge reflex). If he feels it slow down spontaneously, that may be a heart arrhythmia/dysrhythmia. It could be because his heart misses a beat or because something other than the usual tissue takes over.
I mean, there's not a whole lot you can do until you see the cardiologist unless your friend is spontaneously fainting or something. Until he goes to the doc, I'd suggest no strenuous activity, as that can exacerbate arrythmias. Whenever he feels weird, tell him to take a seat and ride it out.