That’s the “dub” you hear—the end of the heartbeat’s working cycle. After the dub , there’s a brief pause. That’s your heart relaxing, refilling with blood, and getting ready for the next lub-dub . The silence is as important as the sound—it’s rest time for your hardest-working muscle. What If the Rhythm Changes? Healthy hearts don’t always sound like a metronome. Your heartbeat naturally speeds up when you breathe in and slows down when you breathe out—that’s called sinus arrhythmia , and it’s totally normal (especially in young people).

But have you ever wondered why your heart doesn’t just make one sound? Or why it sometimes adds a “swish” or a click?

Lub-dub. Lub-dub.