What Causes Constant Beating Pulsation In Hand And Arm?

I am very concerned about the constant beating pulsation which I feel in my right hand and the upper part of my right arm when I rest in bed at night before falling asleep. My last blood pressure reading was 115 over 75. I am a 68 year old man in good physical condition. 6 1 and weigh about 192 lbs. I walk 5 miles each day, walking about 1,500 miles for the year for the last 8 yrs. I am a former college athlete and a 30 year high school basketball coach and I am beginning to feel very concerned about this beating pulsation in my right hand and the upper part of my right arm. I would appreciate your opinion. THANK YOU!