My resting heart rate when I'm feeling good is usually 100-110. When I get sick it is around 120-125, and frequently gets into the 140's/50's if I am up walking around in the hospital. When you say racing, how fast are you talking? I also had AVNRT, which meant that my heart would occasionally break into a gallop around 230+, which was really scary, but I had an ablation in June to fix that and it hasn't happened since.
The typical drug to slow down your heart is a beta blocker, and I've been told by a cardiologist that those might not work for me for 2 reasons. First, they counteract albuterol. So that's no good. Second, my body is getting less oxygen when I'm sick, and my heart is pumping faster to try and make up for it. So if I go on beta blockers to slow it down, then I may not get enough oxygen when I'm sick and I could pass out.
Honestly, I think it's just a result of my heart needing to work harder to compensate for other deficiencies in my body. My goal for 2011 is to really focus on exercise to try and strengthen it and settle it down a bit.