Heart Rate

[cartoc]

When exercising, should you keep you heart rate in the fat burning zone or the cardio zone to lose weight or does it not matter?

[Dominique]

What matters if you want to lose weight is being in a caloric deficit, e.g. at the weekly level. The deficit is your total energy expenditure minus your total intake. Your HR zone while exercising hasn't got a major impact on your total expenditure.

[Bill_k]

Calorie burning numbers increase certain amounts as your heart rate goes up obviously  .Watch the number accelerate when you get into the fat burning zone so yes .

[emili]

keeping your HR up will help burn through more calories at a faster rate. but that doesn't mean you are going to lose weight. as @Dominique  pointed out, being in a deficit is what will help with weight loss.