Swelling of the legs and ankles is caused by fluid accumulation in the body, which can be a sign of worsening heart failure. You may feel that your shoes are tighter than normal if swelling in this area is increasing. The fluid build-up is due to reduced blood flow out of the heart causing blood returning to the heart through the veins to back up. This leads to fluid accumulation in the abdomen and lower limbs and congestion. You are more likely to notice swelling in your legs and ankles later in the day because gravity increases the amount and pressure of blood in the veins of the lower limbs. Lying down and resting for a period will usually reduce the swelling.