An indentation on your leg may be related to edema, which could be a sign of heart failure. Edema is caused by a buildup of excess fluid in body tissue and results in swelling. In heart failure, the heart isn't able to pump all the blood returning to it from the veins, causing that fluid to "back up" into tissues. Edema is most noticeable in the feet, ankles, legs and abdomen of those with heart failure. Fluid can also build up in the lungs.
If you press on your leg for several seconds and an indentation remains after you let go, that could be a sign of edema.
Let your doctor know if you experience swelling or other symptoms of heart failure caused by this fluid buildup, such as trouble breathing or fatigue.