How long has it been 21%? Is it relatively stable at that level,or is in decline?
People react differently to low EF. There can be a number of causes,including high bp. Is his BP controlled well? Also he has a pacemaker, presumably this was to assist heart function? What was his ef when he got the pacemaker put in? Is he able to do any exercise? Presumably he has exercise tolerance issues? Exercise is usually the doctors opening line of discussion. He may need a review of his current medication , and some meds do help boost EF. Dont know if this helps......
It all depends on the cause. If his EF is low from heart attacks (most common) and he is taking his meds, then there is little chance his EF will improve. However, if he recently had a heart attack and has just started his meds, then there may be some small improvement to come.