Hello, thanks for the query. Is your mom a diagnosed case of dementia? If yes, which type of dementia? Since she is receiving Remeron (Mirtazapine); she seems to be suffering from some form of depression or anxiety or both. As such Mirtazapine is fairly safe except for issues of weight gain & deranged lipid profile & hence may not be that good option considering your mothers history cardiac surgery. There are other safer options like escitalopram, sertraline, tineptine for control of depressive-anxiety symptoms. Similarly, risperidone is probably prescribed to your mother to control agitation or other behavioral manifestations which can occur in dementia. Though not entirely safe but if given in low doses & under constant medical supervision, risperidone seems to be OK choice. Other possible alternatives to risperidone which you can ask your doctor are Quetiapine, haloperidol (post your mothers current cardiac status evaluation) or a drug name Trazodone which can take care of depression, anxiety, agitation & all other behavioral problems arising due to dementia. Hope this helps. Good luck