I asked him if I had perhaps suffered a "silent" heart attack -- the kind that damage the heart but you don't know it. He indicated that might be one explanation, and seemed to think that the evidence of damage might explain the left nerve branch blockage. It doesn't sound like an immediately worrisome problem, but it does explain why I have been having breathing problems under severe conditions the last few years.
I see encouraging clinical trials like this, but this sounds like it is intended for people with much more serious ejection fraction problems than mine -- and at this point, the gains are pretty small.
On the other hand, there is this encouraging report of how high intensity aerobic conditioning exercise help to restore scar tissue to working status (the British Medical Journal abstract for the article is here):
Dr Richard Godfrey, a Senior Researcher within the Centre, suffered a heart attack in 2007 in the absence of any heart disease, resulting in 16% myocardial scar tissue. The cause was later found to be coagulopathy - a blood clotting disorder.
Dr Godfrey, who was formerly Chief Physiologist at the British Olympic Medical Centre, undertook 60 weeks of high intensity aerobic interval exercise, three times per week. Sessions involved six to 10 exercise intervals of 1 min hard alternating with 1 min easy, designed to take his heart rate just above 90% of maximum.
Cardiac MRI scans before during and after showed a 50% decrease in the amount of scar tissue in the heart - the first time that exercise has been shown to cause cardiac repair.UPDATE: Obviously, I am going to check with my cardiologist before I start this, but there are advocates for what is called High Intensity Treadmill Training that seems to be related to the exercise program mentioned above. It doesn't seem impossible that the body might be able to repair at least some levels of cardiac muscle damage through an aerobic exercise program like Dr. Godfrey used.