Sometimes my heart tends to beat fast and i sometimes have sortness of breath. what can cause it?

You will need: an examination by your family doctor and/or further tests including blood tests and perhaps heart tests to pin down the cause. I would seek that evaluation sooner as opposed to later.

Tachycardia: Many causes of tachycardia. The shotrness of breath is associated with exertion? Dyspnea on exertion is most often related to cardiac conditions. Tachycardia can be related to heart conditions, respiratory conditions,deconditioning or anxiety/panic. Full evaluation will be helpful