Hey, man. I am a medical student. I'm also fantatic about keeping in shape, and I also have a chronically irregular heart rate. You always have to be careful with heart conditions and working out, obviously. But, chances are your arrythmia is completely benign. If you have a serious problem, you would most likely be having symptoms....fainting, palpitations, chest pain, shortness of breath, etc. The truth is, many young people, boys especially, have irregular heart rates. Athletes tend to have slow heart rates and therefore will often have extra beats, especially when taking in a deep breath. When they begin to exercise, the heart rate rises and is completely regular.
So, if you haven't had symptoms, you're probably fine. You might want to ask for a basic EKG if you haven't already, just to rule out a cardiomyopathy. Here's a little test you can do....next time you climb a few flights of stairs, just feel your carotid pulse. It should be a regular rhthym, and you shouldn't feel light-headed or excessively short of breath. Another question for you is how much caffeine/ alcohol do you drink? They are both extremely excitatory to the heart. While small doses of caffeine can help you have a good workout, too much will make you dehydrated, shaky and your heart fluttery.
So, if you're feeling fine and your EKG and blood pressures are normal, then you should be free to do whatever exercise you like. Your young, healthy heart will be able to accomodate the increased workload, and you probably won't even notice the arrythmia. Stay very well hydrated! Dehydration can make your heart "skippy". And of course, back down if you're feeling light headed! Hope this helps!