驗證網址kidshealth.org安全性

Your Heart & Circulatory System - KidsHealth - the Web's most visited site about children's heal

We Got the Beat How does the heart beat? Before each beat, your heart fills with blood. Then its muscle contracts to squirt the blood along. When the heart contracts, it squeezes — try squeezing your hand into a fist. That's sort of like what your heart d...

網址安全性掃描由 google 提供