a rapid heart beat is quite normal while fasting but soon settles down.............
"The pulse varies greatly during a fast. It may run up to 120 or even higher, or it may drop as low as 40, per minute. Indeed, Mr. Macfadden records a case in his practice in which the pulse went down as low as 20 and was so feeble it could scarcely be felt. It is the usual thing to have the pulse rate increase at the beginning of the fast and then, after a day or two, to drop. In chronic cases that are confined to bed during the fast, the pulse usually, after its temporary rise, drops to 48, or 40, where it may remain for a day or two days and then mounts up again to 60. After a few days it will settle at 60 and remain there until eating and activity are resumed. It is, of course, understood that the pulse is subject to all the variations, while fasting, as at other times of life, and that where there is "disease" of the heart, or nervous troubles, it will often vary greatly from the above standard. Where stimulants are employed during a fast, these occasion more heart activity than if taken when one is eating.
Discussing what, to the uninitiated, are alarming heart symptoms which may arise during a fast, Mr. Carrington says: "I may here remark, however, that such extreme variations invariably denote some profound physiological change taking place at the time--a crisis, in fact. The fact that hitherto weak hearts are actually strengthened and cured by fasting proves conclusively that any such unusual symptoms, observed during this period, denote a beneficial reparative process, and not any harmful or dangerous decrease or acceleration, due to lack of perfect control by the cardiac nerve."--Vitality, Fasting and Nutrition, p. 464. http://www.soilandhealth.org/02/0201hyglibcat/020127shelton.III/020127.ch27.htm
Drink only according to thirst, as any excess is a burden to the kidneys and serves no useful purpose, including inhibiting elimination.