Awesome
Gotta TRI
Erica, I just peeked at your training log. You've got some pretty nice swims in recently but then nothing for quite some time. Either you haven't logged them or haven't done them.
I'm only guessing but I speculate your heart rate is more from nerves than anything else. It's the fight or flight response from being in a foreign environment.
Another idea for a warm up is to maybe start with some drills rather than any freestyle. Practice swimming on your side or finding your balance on your back. And lastly, trying to judge exactly how hard your working in the water can be difficult. When you say your swimming slow you might actually be paddling with everything you have.
A guy who occasional swims next to me swims slow but he takes like 40 strokes to get to the other end of the pool. I typically take 18 - 20. He's probably working harder than I am.