There is absolutely no evidence that cardio is any better for the heart than any other exercise, be it walking, weight training, or playing sports. It does increase free radical damage, however.
The benifits of aerobics are a myth perpetuated by the fitness industry in the 80's when aerobics became popular, and hence, a way of making money for the mags and supp companies.
People who run do not live longer. But they do have more joint problems, shin splints, misaligned spines, and bone spurs in their knees. Even Kennith Cooper, the guy who invented the word "aerobics" admits this.
(Yes, aerobics is a "made up" word. There's no such scientific or medical term to differentiate between types of exercise.)
There's plenty more, but I'm not going to get into it. This will have to hold you.