Here's a 10 second recording of a normal 5 year-old boy's heart, recorded over the left sternal border, and two visualizations of it: the raw waveform, and a Fast Fourier Transform of that waveform. The original recording was made with Sound Recorder, the waveform and mp3 conversion were made with Audacity (and lame) and the FFT was made with Amarok. All done in Ubuntu

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I captured the sound with a stethophone I made out of a Littman Classic II SE stethoscope head, a piece of tubing from a lab, and a lapel microphone from Radioshack.