Yes, doctors can determine if there is pericardial effusion from a heart echocardiogram. Echocardiogram is a test that uses sound waves to create a moving picture of the heart. The picture is much more detailed than x-ray image and involves no radiation exposure. Pericarditis is an inflammation of the pericardium, which is the sac that surrounds the heart. The pericardium normally functions to protect the heart and reduce friction between the heart and surrounding organs. Pericarditis may be accompanied by pericardial effusion, which is fluid accumulation in the pericardial sac.
Doctors can also use an electrocardiogram - Pericarditis and pericardial effusion produce distinctive patterns on an electrocardiogram.
Also, an echogram can be used to determine if there is pleurisy (an inflammation of the pleura, the lining of the pleural cavity surrounding the lungs).
I have never heard of pleurisy causing the face to swell on one side. This is something that I think you should discuss with your doctor as it might be serious.
I hope that I've been helpful, please let me know if you need anything further!
Peace and Blessings
Look For The Good and Praise It!