Will i have a heart attack from heart palpitations due to hyperthyroidism? and will i gain weight when i start taking the medicine to treat it?

No : You won't have a heart attack from hyperthyroidism as fast heart rate is not what causes a heart attack, it's blocked arteries from high blood pressur, cholesterol, and inflammation. Possible to gain weight once you are medicine not of you eat well and exercise.

Depends: On your underlying cardiac status...If ur young and have no blockages in ur heart, unlikely heart attack- but if ur older and have blockages, maybe, bc too much thyroid hormone makes ur heart work harder than necessary- if heart doesn't get enuf blood/oxygen to do that work, that's a heart attack. Ur metabolism is higher bc of the extra thyroid horm, so if u cont to eat the way u r, u might gain.