weight lifting and your heart beat

who ever said that weight lifting isn't aerobic .I was doing my leg workout the other day and decided to use my polar heart monitor(watch)just to keep track of my heart rate .I usually use it for my cardio.

well the results were surprising to me anyways.My max heart rate was 168 bpm at the end of my fucken leg presses.it would come down into the 130's fairly quick after my set .After my press then every exercise got it up into the 155-165 range.

could this be used as a indication of how hard your pushing yourself?
BTw my resting heart rate is ususally around 70 bpm.
.i was surprised to see it go up that high eventhough i push extremely hard during my workouts and go to failure on everything .

any comments,personal experience,opinions etc would be cool.