My heart beat fast sometimes and it may last for few hours I have normal health history. Symptoms are tremor nearly fainting and shortness of breath?

Need to be seen . Despite a lack of current medical problems there are more serious issues that could arise that would give those symptoms. One possibility is a thyroid gland that is overactive or a cardiac rhythm abnormality. To make determination lab testing and examination needs to be done. This should be done immediately considering the seriousness of the symptoms.