Good stuff! Back to it, in phases.

30 trips up and down two flights of stairs, two steps at a time.
Time: 17:15
Avg heart rate: 164

At the 12:30 mark (yesterday's time for 20 trips), I had already done 24 trips up and down, so a fair bit faster pace, plus a 50% increase in the number of stairs climbed.

Now I just need to give up the freaking ice cream. Sugar is nearly as tough to quit as nicotine and alcohol, and a lot easier to fall back into.