I would go with the suggestion that Flycather made re contacting the pacer manufacturer. Two of my friends have had to have their pacers reprogrammed to a slower rate because of feeling fatigued and breathless. I guess this isn't uncommon.
Norma
It's certainly possible that the pacer isn't programmed correctly, but that's just the starting point. It's also possible that the old leads that go to the heart aren't working correctly, it's possible that the pacer isn't working correctly, etc. I have a pacemaker, and had to have it reprogrammed to slow my heart rate down, it was working me at a rate that exceeded my ability to deal with it. I was tired, and breathless. After it was re-programmed I felt very well.
What is the brand of the pacer? All pacer manufacturers have representatives who are available to check the pacer to make sure that it working correctly. If you aren't comfortable with what the doctors are saying, I'd call the manufacturer and get their feedback. I'm a volunteer in a Cardiac wing of our hospital, and the Medtronic, Biometric, etc pacers representatives are always around. That is where I would start.
Question: have they changed his drug regimen lately? That could influence how he feels.
Before changing doctors, I'd talk to the Pacer manufacturer. Have the information on the card he was given available when you call. If you aren't comfortable after talking with them, I'd simply get a second opinion, perhaps at your State's teaching hospital if possible. Keep us informed.