You really shouldn't have problems. In college, I was in this weight lifting and cardio kinesiology class where you'd have to do 45 minutes of supervised heavy weight lifting and stationary biking/treadmill. We even had heart monitors and our BPM's had to be over 150 in order to pass the class for that day, the dick teacher went around and marked everyone's as it was displayed on a watch on our wrist (with a strap around our chest detecting the heart rate).
At any rate, I've rambled. I went to this class after blowing nearly half an ounce of cocaine with a friend from 12 a.m.- 8:15 a.m. (the class was at 9:00). I thought I was going to die in there, truly. Cocaine works the cardiovascular system much more roughly in general than do amphetamines. I survived the workout that day, but that's not to say everyone's invincible. what I'm saying is that, with the moderate amount of amphetamines you say you've ingested, as well as the time lapse between ingesting the drug and exercising, you should be just fine.
My simple recommendation if you intend to use amphetamines during workouts? Just try not to over-work yourself. Pay attention to your body - it's loaded with signal pathways that tell your brain when and where you've over exerted yourself.
However, in the everlasting spirit of harm reduction, I agree with motiv311; it's probably better to try and achieve the "natural high" as would be the product of exercising of one's own will, without artificial stimulation.
Stay safe!
~ vaya