discovery potentially life saving and are calling for a change in blood pressure guidelines. dr. marc siegel of the medical "a" team is joining us right now. so there's this new study out that gives you a better number at what the optimal blood pressure should be, and it's a lot lower than what we used to think. >> this is a life saving study. i come on all the time here, steve, talking about studies. this is one of the most powerful ones i've ever seen. why? because we thought 140 systolic was okay for your higher number. what is systolic? blood pressure occurs when your heart sends a stream of blood out into your arteries. when it's pumping. the heart pumps, and blood shoots out of your arteries. when the heart is resting, in between pumps, that's the lower number. so the higher number is when it's pumping. the lower number is when it's resting. and we thought 140 was okay. it turns out in a high risk group that they looked at of over 9,000 people, over three years, they found that you got to get it as low as 120. and you know what? the results were so dramatic,