There are many possibilities. Some of them include: A) Diseases of heart have to be ruled out, e.g. problems with heart muscle or heart valves are a common cause of both PAC's and PVC's. B) Systemic causes (not related to heart) have to be considered also, e.g. anemia, thyroid overactivity. C) Autonomic and neuro-cardiogenic causes can also have same manifestation, e.g. increase in heart rate with standing because of drop in BP.