The sac surrounding the heart does have a certain amount of fluid, it's there to protect the heart from pounding against the lungs and ribs. If fluid builds up above normal levels, it's called Pericardial effusion. Medication sometimes works to remove the fluid, but sometimes a tube has to be inserted for a few days, to allow the excess to be drained. If the fluid builds up too much, it can cause chest pains and stop the heart working efficiently. However, I'm not sure this would cause leg swelling unless he has heart failure. Some medications such as antidepressants can cause fluid build up, but so can being overweight. There are a few things which can help. Exercising the legs is one, wearing support stockings, and regularly elevating the legs so they are higher than the heart.
To be on the safe side, has your Doctor run blood tests? to check kidney function etc?
Has he been evaluated for any type of heart failure? If there is fluid around the heart, the patient is usually hospitalized and meds are used to remove the fluid buildup. What do they mean by too much medicine? What tests have been done for him? Ally