My husband & I have a walking route that we walked before I was pregnant that was almost 3.5-4 miles. In my first trimester, I made it 1 mile & was out of breath & tired! I talked to my doctors nurse & she said that it's completely normal since your body is pumping more blood for the baby.
My resting heart rate is usually between 60-65 bpm. Now that I'm pregnant, it's around 80 bpm! So yes, it's normal. If you feel like it's an issue, I would call your doctor- as in any other concerns you might have! Good luck!