RESUMEN
<p><b>AIM</b>To study the effects of the 50 Hz-filter circuit in a microelectrode amplifier on cardiac action potential waveform and parameters.</p><p><b>METHODS</b>Cardiac action potential signals were fed into a microcomputer through a glass microelectrode, a microelectrode amplifier, a differentiator and A/D converter. The cardiac action potential signals were recorded and analyzed with 50 Hz-filter circuit and without it, and the frequency spectrum in the signals was analyzed with the fast Fourier transformation.</p><p><b>RESULTS</b>When the 50 Hz-filter circuit was used, the phase 0 of the potential waveform was seriously distorted and prolonged. The maximal rate of depolarization at the phase 0 was cut down, while the other parameters were not effected.</p><p><b>CONCLUSION</b>There has already been much 50 Hz element in the action potential waveform. During amplifying the cardiac action potential signal, the 50 Hz-filter circuit should not be turned on. Otherwise, the experiment results will be effected.</p>