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Post: For reading the heartbeat you are going to need a fast sample rate as you will need to measure the time in between the pulses. The ADC Pi Plus and ADC Differential Pi are probably going to be too slow for this as the maximum sample rate is 240 samples per second. The ADC DAC Pi is faster at around 12,000 samples per second which should be fast enough to get a usable reading. As a heartbeat is basically a logic signal, the heart is either beating or not, a better approach may be to use some opamps to build a comparator circuit which triggers when the heart beats. You could then connect this directly to one of the Raspberry Pi GPIO pins and configure the pin as an interrupt so a function is called every time the heart beats. You would then just need to measure the time span between the function calls to work out the heart rate. This would have the advantage that the processor would not be tied up with taking voltage samples between beats like it would be using an analogue to digital converter and the accuracy would probably be higher as you could measure the time between heartbeats down to the millisecond. I have never tried measuring galvanic skin response but most of the circuits returned from google appear to use opamps to amplify and condition the signal before passing it into an ADC. Any of our ADC boards should do the job of measuring the voltage but as you will be using the opamps to set the voltage limits I would probably recommend the ADC Differential Pi. It is more accurate than the ADC Pi Plus at measuring small voltages and it is slightly cheaper. If accuracy is not an issue then the ADC DAC Pi would do the job and the two input channels would give you one for temperature and one for GSR.