Abstract: A method and apparatus for removing baseline wander in which an ECG waveform is continuously sampled at 500 samples per second. The digitized data is continuously filtered by an infinite-impulse response (IIR) filter implemented on a first microprocessor. The data is stored in a buffer from which it is read in reverse chronological order in overlapping 3 second blocks. Each block is applied to the input of a second IIR filter which is implemented on a second microprocessor with substantially the same code as the first IIR filter. The first 1.5 seconds of each reverse-filtered block is disregarded to permit the output of the filter to settle. The retained data is stored in a queue from which it is read and displayed on a monitor or printed with baseline wander removed.