Emulation of soundcard filters with Arduino

No, I don't.

However, if you look at the page you found yourself more carefully, you will see that everything is already in the schematic.
Apparently they use a "MCP6001" op amp as stated in the right of the schematic.
The filtering seems to be a worked out version of a simple low-pass filter.
(See Low-pass filter - Wikipedia for details about this.)

Also, if you check the blog they link too (http://pulsesensor.com/2011/08/01/anatomy-of-the-diy-heart-rate-monitor/), you will find the older version, which is easier to understand.

Good luck with your project!