I had an ablation done in November 2011 to correct SVT. Overall, it wasn't that bad, but definitely not something I would want to go through again (who would!). I'm also a baby when it comes to pain and had never had any previous surgeries
Here's a brief recount of my experience (obviously I'm not a doctor so I'm just telling you what they did for me). They insert an IV into your arm before going into the operating room. When in there, they lay you down on a table that has two arm rests. They then put the stints in, which for me was the worst part. They put 3 stints in your groin, and then one in your arm. They numb the areas, thank goodness. I had asked for some sort of sedative medicine since I was super nervous and never had surgery before, but they didn't want to give me anything since it might affect the way my heart responds to the ablation.
After that, they feed the catheters through the stints. From your groin, they feed them up to your heart. It doesn't hurt, but feels really weird. That only takes a couple of minutes.
Overall it lasted about 3 hours. The whole time I was watching what they were doing on the monitor which was both kinda gross and kinda cool. They just kept moving the catheters around and sending electric currents through my heart to try and get it to induce tachycardia. Once they can pinpoint the areas that are conducting electricity that shouldn't be, they ablate (aka burn) them. That only lasts a couple seconds but it's pretty painful. At first you just feel really warm, and then it's a sharp pain for like a second and then they stop. In the 3 hours they had to ablate 5 times (and they told me that was a lot, normally it's less than that). So it's mostly a lot of just lying there while they move the catheters around, make your heart beat fast, etc. Again, the whole experience is more tiring than painful. Just having your heart beating fast then normal over and over again was tiring.
After it was over, you have to lay for 2 hours in the recovery room in order to give the groin area that had the stints in it enough time to clot. After that I just headed home and rested. It took a couple days for the groin area to not hurt anymore. It also takes some time (weeks to months) for your heart to completely heal after it. At first, I would get out of breath EXTREMELY easily, and it took a little while for that to go away.
It's been a year and I haven't experienced tachycardia since the surgery (knock on wood). I've been dealing now with a very strong (not fast) heartbeat - which the doctors can't figure out yet if it's stress-related, or a result of the surgery.
Anyways, I'm done rambling! Good luck with your surgery! Take it from someone who can't handle pain, it's not all that bad, and it's definitely worth doing.