Hi, Thanks for writing in. The pleural space is a free space between the lungs and thoracic cane. Similarly the pericardium is a free space between heart and its covering. These are potential spaces for collection of fluid in disease. As you had thymic cancer and heart problems, it is important to know the type of fluid getting collected as pleural and pericardial effusion. Little amount of pleural fluid can be taken out with a needle and tested for its nature. If cancer cells or any infection is found then treatment must include medicines for it. If large amount of fluid is collected then it must be drained slowly by using a intercostal chest drain tube. It must be done under medical supervision and slowly. If at anytime you are feeling severe shortness in breath when fluid is being removed then it should be stopped immediately. Slowly removing the fluid will allow the lungs to expand back normally. Medicines can also be given to cause drainage of fluid by creating increased urine production. Please do not worry.