Brian good luck with your quest. I have been battling the same issues these past months. Just due to old age I think I was recently prescribed Blood Pressure medication and it does of course affect performance. I can't get my heart rate up beyond a certain level and thus my body can't work efficiently. Beta blockers definitely throttle down a heart rate.
I'll check with some of my doctor friends for a cardiologist they would recommmend. One recommendation: if you are going through a health insurance plan through work, it's best to rely on who is in their network and attached to a hospital (say St. Joseph, Hoag or Mission) you would prefer treatment at. I have learned their my own health struggles that the doctor listed inthe plans are generally top notch, all board certified, experts in their field. And I have also learned you don't want to select someone not in the plan.