I agree with Amanda. I've had several clients with them, one thing to check is how long since it's been put in or serviced (wouldn't want to do too close to that) and it's always good just to ask what they have been told about monitoring their own activity. To be honest, in most cases, if exercise hasn't been restricted I think that puts much more of a strain on a person than a massage.
Only other thing to be aware of is any electrical equipment you use. I occasionally use electric massager or audio sonic which are strictly contraindicated with pacemaker, and I would even be wary of using an electric heater if your couch has one (not sure if that would be a problem, but better safe than sorry.) Also, if for any reason you use a microwave (can't think why you would - but who knows!) that's also strictly contraindicated.