My calf and ankle are fine when walking but when i sit with my feet up the pain starts in my calf.what causes this?

Not enough info: If its always related to after walking it is probably cramping related to exercise. However, if it persists your physician needs to rule out circulatory or skeletal issues.

Calf pain: This could be from spinal canal stenosis of the spine. You might benefit from an MRI but see your doctor and have him examine you before.

Tendon: It is hard to say but this could be a tendon that gets stretched when you sit. Is the calf tender. Occasionally we could be worried about a blood clot. When you see your physician these are the things that will be looked at.

Pain in the calf.: Calf pain that goes away when you are walking and hurts when you have your feet elevated has some elements of concern. Certainly, the problem could be related to the tendon and/or muscle, but that is less concerning that something else. Calf pain, not ankle pain, can be a symptom of early peripheral vascular problems. This is easily checked by a vascular specialist. Remove doubt and find out.