Target heart rate?

Can anyone direct me to a site that explains heart rate and what target I should be aiming for when I’m doing a cardio workout? I think possibly I am getting into better shape (though still haven’t lost any weight … sigh) and am not pushing myself to work harder. This is a good thing, but I want to know where I should be.

http://www.health24.com/fitness/Cardio/16-1371-2173,30883.asp

http://www.changingshape.com/resources/calculators/targetheartratecalculator.asp

http://www.livestrong.com/article/90858-heart-rates-cardio-vs.-fat/

They all say take 220 and subtract your age. That’s your Maximum Heart Rate (MHR). You should work out so your heart rate is 60-80% of that.

So I’m 44. 220-44= 176. My heart rate shouldn’t go higher than that.

I should work out so my heart rate is 106 - 140. (multiple the MHR by .6 and .8 to get the percentage).

I did a Google search for “Cardio Heart rate goal” if you want more info.