Figure 2 A computer is connected to a power amplifier to an infrasound woofer, which is mounted at the top of the test chamber, which is specially constructed to allow levels of infrasound up to 130 dBz and houses the muscle investigation system inside of it. A measurement microphone is included to ensure a steady level of infrasound throughout the experiments. The cardiac sample (M) is brought inside, where it is electrically stimulated to perform pulsatile contraction at a frequency of 75 bpm, simulating a working human heart. The contraction force and duration are measured then.