I almost always experience an intermittent rapid heartbeat when I am fasting. I have always thought it was a good sign that toxins or parasites were clearing out of my heart. If it became painful, I would make myself a cup of hawthorne tea. If fast palpitation lasted so long it made me dizzy, I would apply firm pressure below my nose/above my lip. That pressure point will usually stop a tachycardia attack. Then I would put one drop of LugolsIodine in my next glass of water because Iodine deficiency is frequently the cause of tachycardia. Unless you are so terribly weak that it is getting difficult to talk, because you run out of breath easily, I don't think you need to worry about this being a starvation issue.