Chest pain and heaviness in legs when going up stairs, what could it be?

You may have angina pectoris, which occurs when the heart muscle needs more blood than it is getting during times of physical activity or strong emotions. It is very important that you get examined at an Urgent Care Center or Emergency Room as soon as possible to check for angina & other possible illnesses. Try to avoid too much exertion & get to a medical facility now. I wish you the best!

These symptoms might represent significant coronary artery disease, the possible precursor to a heart attack. And there is some urgency to getting a correct diagnosis. Therefore, the best approach would be an immediate evaluation by a specialist: Either a cardiologist or emergency room physician; need an EKG, cardiac imaging, careful history and phys exam, blood tests; it's urgent.