Heart Rate and Conditioning

I'm curious, how many of you use, and how often do you use it, taking your heart rate to judge your aerobic conditioning? Last winter when I was not in good swimming shape, my heart rate for a medium effort swim would run 160 beats per minute (I'm 59, not a good heart rate number). As my aerobics came into play, it would drop week by week, a good thing. Today, I am swimming 10,000 yds every other day and on off-days do a little mile or two with a half-mile of sprints. At the end of my 10,736 yds yesterday, my heart rate was 110. Also, I took my resting heart rate yesterday morning and it was 40. The thing I notice is the better condition I am in, the faster my elevated heart rate falls and I have heard this is a good sign. Now, I take my heart rate each and every day before, during, and after swimming. It gives me a lot of information. How about you? Are you doing this often enough?