angina stops with exercise

I'm a 62 year old male, non-smoker, low BP, high cholesterol well-controlled by statins, 5'10" 170lbs, regular exerciser.

I've had moderate, stable angina for about 6-8 years. I've had two angiograms, both negative for CAD. My coronary arteries are clear, acc'd to my cardiologist. Ejection fraction is 60.

Here is the angina trigger: When I begin to exercise-run or treadmill for example, I get classic angina symptoms, chest pain, neck, left arm down to the wrist, moderate but very uncomfortable. During a stress test my cardiologist noted a change in  my EKG that concerned him, which prompted the first angiogram 3 years ago. If I continue at a moderate pace the angina disappears-like clockwork, beginning at about 13-15 minutes, and by 20 minutes it is completely gone. I can then push myself to the limits of my heart and respiratory rate. Once I  get "warmed up", start sweating, everything is fine.  Exercising within 2 hours after a heavy meal, however, will slow that process down considerably.

I am a hiker/backpacker. My first 15 minutes on the trail may induce some angina, but once that passes, I can go full bore, up hill for hours with no pain.

My cardiologist says something like, "well, maybe the little regulator in your heart takes some time to get going". Basically is telling me he's not sure whats going on. Is there some sort of regulatory process that needs to warm up and increase blood flow to the heart? Can it indeed lag a little when demands are placed on the heart?

Two questions are nagging me: 1. What is really the problem with my heart? Obviously there is some cardiac muscle that is ischemic for a time, but after 20 minutes is not.
2. Does this portend a future problem? Will this get worse over time? Am I endangering myself by pushing myself hard during exercise?

Any insight would be helpful, Thanks

[kenkeith]

The problem could relate to the delivery of oxygen.  In most tissues of the body, the response to hypoxia (reduction of oxygen despite adequate perfusion of the tissue by blood...stress test negative) is vasodilation. By widening the blood vessels, the tissue allows greater perfusion (negative stress test). By contrast, in the lungs, the response to hypoxia is vasoconstriction. This is known as "Hypoxic pulmonary vasoconstriction", or ***"HPV".  After warming up the respiratory system is normal providing ventiltation and perfusion match.

***Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism unique to the pulmonary circulation that allows redirection of blood flow to alveoli with higher oxygen tension, thereby reducing ventilation/perfusion mismatch.