Most people who have heart failure need to restrict how much salt (or other sodium containing products) is in their food. This is because sodium makes the body retain water which goes into the circulatory system and makes the heart have to work harder to pump all the extra volume around.
Many people find they also have to cut down on how much liquid they drink. Restricting the salt and other sodium containing foods to 2000 mg daily is often recommended, as is limiting fluids to 2 quarts daily. Your health care providers should help you determine how much of a restriction is necessary.
People who have heart failure due to coronary artery disease or narrowing of the blood vessels, may also need to restrict the amount of fats that are in their food.
There are many good books available to help you prepare good tasting, low-salt, low-fat foods at home. Nutrition specialist are also available to advise you. Getting good information is particularly helpful if you eat out frequently or rely on frozen pre-packaged foods.