Humans walk very efficient. If you want to burn fat or get your heart rate up, a 20 second sprint is equal to two hours of walking.
If you want to increase the capacity of your cardiovascular system, to get a lower resting pulse, the best method is to engage in an activity that gives you around 70% of your max heart rate, for about 45 minutes or more. Examples of such activities (for normal people) is gym training, cleaning the house, mowing the lawn, etc. At least twice a week.
Max pulse is around 220 minus age. So if you are 35, you want to average (220-35)*0.7=130, witch will feel easy.
If you want to increase the capacity of your cardiovascular system, to get a lower resting pulse, the best method is to engage in an activity that gives you around 70% of your max heart rate, for about 45 minutes or more. Examples of such activities (for normal people) is gym training, cleaning the house, mowing the lawn, etc. At least twice a week.
Max pulse is around 220 minus age. So if you are 35, you want to average (220-35)*0.7=130, witch will feel easy.