Go see a doctor, preferably a cardiologist. It sounds like PAC's, or premature atrial contractions. Your atria fires an extra beat...that's the 'fast' or double beat you feel, then a pause, then a really hard couple of beats, which is the ventricals clearing the extra blood that built up. I had these, that ended up turning into atrial fibrillation...a much longer story.
Despite having used steroids and DS's in the past, I don't think either played much of a role in my heart problems. I've researched the conditions extensively, and never found anything to connect the two. I do think that body builders and other athletes will have these issues more than the general population. From what I've read, inflamation can be a contributor, as can increased heart rate variability.
Back to my point, get to a cardiologist, and get a 24 hr holter monitor...its about the size of a pack of cigs, and it records heart beats for 24 hours. Hopefully, they'll catch the missed beats, so you'll know what's going on. PAC's are really common, and afib is becoming more recognized...neither are the end of the world, but you need to know what is going on.
Toby