Suggest Treatment For Muscle Weakness

Hi, Doctor. My mom is currently complaining of muscle weakness, particularly on the left hand side. When I measured her blood pressure on both of the right and left hand side, they were normal and within the same range of 120/80. However, when I measured her heart rates, they were different. The right hand's heart rate was 80 and regular. The left hand's heart rate was thready and 60. I am wondering what is the cause.