I know this is probably way too glib, but a quick search of only the first page of this study revealed no less than 20 occurrences of the word "excessive". Like I said, this may be a cheap shot, but what I take away from this is, don't be "excessive".

See my experience is the absolute flip side of what fried-bake describes. Prior to my conversion to healthier habits, I was a poster boy for all that's evil in the typical American lifestyle. Getting into cycling, along with smoking cessation and marked dietary changes did wonders to mitigate the risk factors I'd indulged in for 40+ years, but of course, nothing cures cardiovascular disease once you've got it. Which is why I quite literally dropped stone cold dead one morning after an easy short ride to the local Peet's to meet up with my riding group. Long story short, I was successfully resuscitated, and underwent an equally successful double bypass graft. Afterward, I had occasion to ask my cardiac surgeon what role, if any, my 100+ mile/week (about 33% of which was done at a tempo or higher intensity level) played any role is what happened to me. His response? "Damned straight it had something to do with it. Had you not been that well conditioned, you would have had a less than 3% chance of surviving the event you sustained. As it is, despite that, your myocardium suffered very minimal damage." He went on to tell me to rehab gradually at my own rate, but to continue towards the same level of conditioning I enjoyed prior to my SCA. It's taken 2 years to get most of the way back, and this is probably as good as it's going to get. That said, I'm still more fit that the vast majority of folks 5 years younger. When I last saw my cardiologist 8 months ago, and his parting shot was to tell me he didn't need to see me again unless I felt I needed it. And to keep riding.

The point is this. Whether or not a given level of training is going to cause cardiovascular pathology depends intrinsic factors that are not at all well understood. I mean, what's the difference between some one who smokes 2 pack a day from his late teens on and lives a happy life into his 80's and someone else who presents with end stage pulmonary carcinoma with only a 15 pack-year history? No one really knows. These studies only document the occurrence of CV is people who exercise to "excessive" levels. This does not establishes causation. It only point to the need for further study to determine what, if any, relation the two have to each other. Remember that. Also keep in mind that what's excessive for one person is just fine for someone else. Like I said before, be honest with yourself and your body, and make moderation your byword. Do that, and I think you'll be fine. Whatever... It works for me. As always, YMMV