Their resting heart rate and oxygen consumption will change based on their size and body temperature. Going back and checking some comparitive physiology notes I still have laying around, an average sized adult BP (1500-2000 grams) will ventilate about 5-10 times per minute and heart rate would be around 40-45 BPM at rest at about 80 degrees. These numbers are based on studies done on a number of squamate species and not necessarily BPs, so there is some room for error, but that should give you an idea.