I have had hypothyroidism for 20 years and have been reasonably well on the meds I am on except for becoming very breathless just recently. I am taking 120 mg of Levothyroxine and 20 mg of Liothyronine a day. Yesterday I had the results of my blood test and my TSH was 0.02, FT4 was 14.7. I had asked for T3 test but they never do it, even though my Doctor makes a special request for it and marks the form "patient not converting". My Doctor was not keen to reduce my Levothyroxine because my TSH is on the low side. She has also arranged for me to have a chest xray to eliminate any problems in that direction and following an ECG which only showed the right side of my heart was a little larger than the left, she is arranging for me to see a cardiologist. However, I wonder if anyone else with an under active thyroid experiences severe breathlessness, I need to do very little, just going up the stairs and I have to sit down until I get my breath back. I would appreciate any help.