The second describes the same thing:

> Several middle-aged and older men trying to improve their physical fitness by weightlifting have presented for repair of severe mitral regurgitation, some of whom stated that they remembered feeling a pop in the chest while weightlifting, which was the start of their dyspnea.

> Arterial BP increases most during weightlifting that is accompanied by mechanical compression of blood vessels (such as when bent forward at the waist or squatting) and when accompanied by a Valsalva maneuver.

Neither of these papers link them to muscle mass but to the stress of high-intensity exercise itself, which I have already addressed.

I agree that we should not assume things, but in the lack of cursory evidence, I would still stand by my argument that in the normal case where muscle mass is formed from working out, such workout stresses and modifies the cardiovascular system to such an extent the result is a body that is more than capable of handling whatever stress that muscle at rest imposes on the heart.

Once again I reiterate my cursory evidence to my argument, that athletes' cardiovascular system are generally so much more efficient and less taxed than the general population that their hearts beat at 3/4 the average heart rate.

It seems like athlete's heart syndrome is a benign condition.