ICDs and pacers are different. With ICD, one has to be concerned with travel of current between the lead and the can (jargon for the generator, not sound suppressor
), so left sided placement is beneficial. With pacer, side of insertion is irrelevant.
I would not recommend positioning the buttstock over pacemaker pocket. The cans are robust, yet I wouldn't subject it to recoil if I had one, for fear of damage to it and, in your case, bleeding into pocket (see below). Hopefully, yours is on the other side.
The valve itself, however, shouldn't present any issues, at least, any that I know of. You do need to know that some valves fail at suture line and develop paravalvular leaks, at times leading to re-do surgery. I am not aware, however, of any studies linking valve failure to exposure to concussion or vibration. Usually it takes some time for stuff to heal and endothelialize inside the heart, but after that, it should be fine. I'd actually talk to your CT surgeon, not cardiologist, about healing times. I can tell you that with bioprosthetic valves we prescribe Coumadin for 3 months, assuming that after that all sutures etc. are covered with endocardial tissue.
You mentioned that it is ticking like a watch, which makes me believe it is a mechanical valve, probably St. Jude's. If that's the case, then you should be taking Coumadin. Some folks get bruised easily, and everybody bleeds easily with even small trauma. Bleeding in pacer pocket is not fun thing to have.
That's all I can think of; will post more if anything else comes to mind.
PS. You didn't say when the valve was replaced so, if it is recent, then you need to let your chest wall heal. I'd not shoot for as long as you're not allowed to drive.