What does it mean when your dr, tells you your heart is functioning on 25 ?

While not sure what the doc meant, many times such numbers relate to the ejection fraction (EF) which refers to how well heart is pumping up blood. A 25% will be in heart failure range with 40% being considered at the lower limit of normal. Such information is extremely useful in dynamics as well, is the number dropping or steady, feel free to ask your cardiologist at next visit.