case study - swelling in the face, tried benadryl-no impact, went to emergency room, has dyspnoea on exertion, had full blood panel for kidneys, lungs and heart, hepatobiliary, urinalysis, ekg, heart failure, CPC, chest x-ray - all these tests came back negative... took diuretic and lost 4 lbs in 24 hrs, hints: this test can't be done at emergency care center, and requires no blood work, performed in a "special" place, and patient has to be put in condition that mimicks symptoms (test challenges body) Which cardiovascular-related test is next?
You want to a do a stress echocardiogram which is a specialized version of a stress test - it can be done either chemically or on a treadmill.  The echocardiogram would give you information about the contractility of the heart muscle, both at rest and with stress; and the valvular function as well as pulmonary pressures which all could be implicated in the symptoms described.  You did not mention the age of the patient in your case, so I wouldn't further hazard a guess on the etiology of the symptoms.
You will have to check with your doctor. Not all family doctors have the necessary equipment to do allergy testing.