You questioned more detailed information on requirements when interfacing electronic circuits to human beeings.

Since I´m head of the development department of a company which develops and manufactures patient monitoring equipment here in Germany, I´m quite familiar which all these requirements. The most relevant standard is the IEC601-1 (=EN60601-1) for medical electrical equipment. This standard defines certain limits on clearance and creapage distances, on leakage currents, on high voltage tests, etc. Additional to this standard exist a number of detailed standards for the various parameters (like ECG) or for combining medical and non-medical equipment.

As you already mentioned this is a very interesting field, but one has to be extremly careful when designing such systems. Nevertheless there are a number of applications for 8051-compatible uCs in medical equipment.

PS: The is an ECG-database available on CD-ROM from the MIT. Sorry don´t know the URL for more info.