Vascular deterioration in the chest is only apparent during exercise. When the damaged vessels inside the chest are stressed by exercise, they fail to send sufficient oxygen to the other organs from the lungs. Damage to the blood vessels in the chest is caused by long-term Covid and many other viruses. This vascular damage cannot be seen with standard heart tests. The clinicians need to be monitoring blood flow inside the body, during exercise to see the lack of oxygen.
The damage that causes exercise intolerance means oxygen has been cut off by vascular insufficiency. Viruses can have the effect of deteriorating the vascular infrastructure between the heart and the lungs.
The intermittent characteristic of the vascular collapse has been diagnosed with an invasive cardiac test iCPET. All the regular cardiac testing shows a normal heart, and normal organs, and people who go to the doctor or hospital are sent home saying they are normal, but they are not, during movement, the blood vessels between the heart and lungs collapse, preventing the heart from getting enough oxygen during movement, during exercise.