Why wouldn't light cardio be recommended?

[orlando.abascal]

I mean it would cause blood vessels to dilate and more blood to reach the affected areas, blood pressure would lower causing less pressure on the area, etc etc. So what is the reason they say to avoid cardio for weeks?

[radio]

I've also wondered about the strict "no physical exertion" rule after surgery. I can understand weight lifting and serious exercise, but why is—for example—riding a commuting bicycle not allowed. How does exercising your legs have implications on your chest, or upper body?

Doctors? Anyone?