I\'m looking for a C# .NET library for digital filtering (lowpass, highpass, notch) to filter ECG waveforms in real-time. Any suggestions?
As far as I know you can write your own, because I did.
This should be a good starter for you (coded in C++ but you can easily covert the syntax to C#) - http://www.codeproject.com/KB/cpp/ecg_dsp.aspx
Third party libraries wouldn't be very flexible on the filter equation parameters. As you only will know the characteristics of your signal (amplitudes, frequency band and sampling etc.)
I recommend using a waveshaping algorithm first to get a smooth signal on the C# side before you apply filters, if your ECG sampling rate is low.