My Husband, 64 Yrs. Has Been Short Of Breath Upon

My husband, 64 yrs. has been short of breath upon light exertion, pale, occasional lightheadedness, and some tightness in chest, we have had pulmonary CT, and Stress tests, a heart catherization and echocardiogram, and carrotted artery ultrasound, all came back with no problems detected, heart has good valves, pressure, etc. but symptoms persist... cardiologist is not sure what to advise next