Swelling or pain in the upper abdomen (stomach area) can occur due to fluid build up (congestion) in the body, which is a sign of worsening heart failure. The discomfort is due to fluid retention and congestion in the liver and gut. Some people who develop swelling in their abdomen notice their clothes feeling tighter around their stomach area. To help prevent this from happening you should reduce the salt in your diet and limit the amount of fluids you are drinking, as recommended by your doctor.
If your doctor or nurse has discussed with you how to adjust your diuretic medication then you should do this if you notice swelling of your abdomen, especially if you have noticed weight gain. Otherwise call your doctor or nurse for assistance.