Picking arbitrary numbers, here's an illustration:

17 lb bike + 123 HR + 15 mph over 20 miles

34 lb. bike + 145 HR + 11 mph over 10 miles

So in thinking what ZenSo, Irulan and GLC has suggested, I may not get equal cardio benefit but I will increase strength to power ratio?

I keep thinking of all those fitness equipment commercials where they advertise quicker fitness in less time by doing more work in less time (i.e. heavier weights, less repetitions). If my heart is challenged more over a shorter period, I'm wondering if I can equal or gain cardio benefit in return.

I don't mean to sound like a broken record, I'm just perplexed. Any physiologists are welcome to chime in.