My (I'm 62) heart problems started in May 2015, till about 5 years ago I ran 5 and 10k races but would at times seem unable to exchange enough oxygen. I had mentioned this to some doctors, but they didn't seem too concerned. Perhaps they thought it was my running style.
Fast forward to July 2015 and my heart cath provided my answer, results were, right coronary ectasia with absent left coronary artery anomaly.
Doc says my heart is poorly plumbed but it works and that is what is important. Considering all my life I have worked and played hard, the Doc might be right when he said I've been lucky.