A doctor tord me that my pacemaker work at 30% of the time is that a lot and it's mean what?

Sounds OK: Pacemakers are programmed to deliver an electrical impulse to cause a heart beat whenever your heart rate goes below a certain "programmed" rate, usually about 50-70 beats/minute. Your doctor's comment indicates that your own heart rate falls below your programmed rate for 30% of your heartbeats, and your own heart rhythm is sufficient for 70% of heartbeats.