Every person alive depends on a fist-sized muscle that contracts roughly 100,000 times between sunrise and sunrise again.

Carley is a writer, editor and social media professional. Before starting at Forbes Health, she wrote for Sleepopolis and interned at PBS and Nickelodeon. She's a certified sleep science coach and ...

S1 and S2 are the normal heart sounds you hear when the heart valves close. Heart murmurs are extra sounds that can be heard during systole, diastole, or as a continuous sound. S3 and S4 are abnormal ...