I am not 100% on this, but in terms of mathmatics it doesnt make sense to "try and slow your heart rate" for fatloss. When your doing cardio for fatloss your working to increase your energy output, by doing so your air intake increases, your heart rate increases, your body works harder, and you burn more calories then you normally would.
It would stand to reason that if your heart rate isnt significantly increasing, niether will your calorie expenditure, and inturn less fatloss. That being said, there are a lot of other factors that go into fatloss. That and the "fat burning zone" you see on most elipticals and tredmills is bullshit.
I don't do this for my family, my friends, women, accolades, pride, or ego. I do it for me and no one else, its just part of who I am.