I m a 42 yo woman. I m having shortness of breath and dyspnea on exertion with walking and talking. gets progressively worse the more i walk or talk. My heart rate drops to around 50 when this happens. my chest gets tight. O2 sats stay at 99% however. Once I stop moving and rest pulse rate recovers. It has been getting worse and happening more frequently. Ive been feeling sick for 2 months. NO one can put a finger on it. Blood work negative except for WBC elevated at 11.2 and MPV elevated slightly. no lyme, CRP normal. found a lump in my right breast but Mammography with U/S said it was an enlarged lymph node with no malignant signs. Had a chest X-ray yesterday awaiting results but they would ve called if they saw something. I have history of SVT but that s rapid heart rate. I take Toprol XL 25mg QD for the SVT, Topamax 200 mg QD for hx of migraines and Vyvanse 70mg for ADD.