I have mctd and was suspected of having PH after failing all the pulmonary lung function tests. It was so bad that I had a right heart catherization only to find out my problems were being caused by the extreme weakness of my muscles. As I made a physical recovery over several years all my lung problems disappeared.
Do you have weak muscles anywhere? I would have it looked into in case it is something else. UCtd is like a preliminary diagnosis when autoimmune symptoms are not clearly one thing or another. It often develops into a distinct diagnosis like mctd which is sle lupus, polymyositis or dermatomyositis, scleroderma. I Have pm and lupus but not scleroderma. Interstitial lung disease is common with overlap diseases like mctd but can manifest in different ways or not at all. Trying to self diagnosis based on the internet is dangerous at best. If your pcp thinks there are pulmonary or heart problems you should see the appropriate specialist. List any clinical symptoms you are having as well as both heart and lung are usually not silent problems.
MCTD (SLE Lupus, polymyositis, scleroderma). Diagnosed 2005. Kidney, liver, GI tract, dysphagia, raynauds, barretts esophagus, quadriplegic in 2005. Recovered and now active in downhill skiing, golf, hiking. Meds: amlodipine, benezapril, omeprazole, potassium, folic acid, vitamins, maxide.
Remain Optimistic and you can overcome.