The first heart sound, or S1, is the "lub" of a normal heartbeat. It's a high-pitched sound that occurs at the beginning of systole—when the heart pumps blood out of the heart into the lungs or body.
There are no shortages of signs, alerts, and passenger announcements during even a routine flight. But in a recent TikTok video, airline pilot @captainsteeeve addressed one question that’s likely on ...