cycling vs walking

[taurushead]

and.

i normally cycle about half an hour a day. but in a new job i don't have time. i walk to and from work, which is about an hour all up , and thats roughly the same 'calories burned' as my half an hour light cycle..but im just wondering if the benefits of going 'harder' for a shorter time (even if its just slightly harder) are important for heart health? should i make time? or is exercise exercise???

[Bof]

According to my treadmill manual, you need to keep your heart rate at 50-59% for heart health, 60-69% for weight loss, 70-79% for aerobic fitness and 80-89% (!) for anaerobic.
(Your max is 220- your age)