What Causes The Lub Dub Sound Of The Heartbeat _top_ May 2026

Lub-dub. Lub-dub. Lub-dub.

She drew a quick sketch on the exam paper: four rooms, four doors. “The lub is the first sound. It happens when your heart squeezes to push blood out. Those two big doors at the top—the mitral and tricuspid valves— snap shut. Hard. Like slamming two car doors at once.” what causes the lub dub sound of the heartbeat

“Exactly. That’s your blood saying, ‘No going back!’” She tapped the paper. “Then the heart keeps pushing. Blood shoots into the big pipes—the aorta and pulmonary artery. The second sound, the dub , happens when the heart relaxes. Those two exit doors—the aortic and pulmonic valves—slam shut. Dub. ” Lub-dub

“Perfect,” she said. “Your doors are doing their job.” She drew a quick sketch on the exam

“All day, every day. Two pairs of doors, slamming in perfect sequence. Lub from the incoming valves. Dub from the outgoing ones.” She paused. “Unless something’s wrong. Then it’s not lub-dub . It’s lub-shhh-dub , or lub-dub-whoosh . That’s a murmur. A leaky or stiff door.”

“So it’s not the muscle,” Leo whispered. “It’s the valves. The doors.”