Nevermind you're right... and I'm a little right....
http://circ.ahajournals.org/content/84/6/2376
Ablation is radiofrequency (think microwave oven) or cryo, not radiological. So there is no radiation exposure per se.
That being said: the original question is unanswerable.
Send me back to school for 6 years... gimme another 5-6 years of training behind that... let me poke around your arteries for a few hours and THEN I would feel better answering that question.
As you may already know, the purpose of the procedure is to sever or interrupt errant electrical pathways that cause the particular arrhythmia. Tiny burns are made in the heart muscle which casue scar tissure to form and literally block the electrical signal in the nerve branch. Multiple ablations can be done throughout the heart or may focus on a particularly troublesome spot. Becasue of the nature of the procedure, success may not be guaranteed on the first try, and repeated attempts may be necessary. Aside from the invasiveness of the procedure, I suppose one would have to consider the amount of radiation received from multiple procedures.
I've had 3 and opted not to have any more. My heart is still a bit erratic but it's better than it was. One person a few years ago claimed to have had 6. I don't know if she had ablations or just EP studies. There's a bit difference between having a rhythm checked and actually having them burn spots in your heart. I haven't heard of a maximum number that is considered "safe."