Could you explicit your question and the goal ? thank you. And how you intend to record the fields.

I was reading briefly about biomagnetism and the fact that both our brain and heart can possess their own magnetic fields. We can detect and measure the heart's using MCG(magnetocardiography) and the brain's with MEG. I don't have the resources to implement a study but my goal is to compare the different strengths of fields produced by the brain and heart and examine their mutual influence on each other, whether it is antagonistic, additive or synergistic, and how the rate of blood flow moderates such activity. Has any research been done on these aspects?

It is very similar to the coregistration of EEG and ECG: ideally, you disentangle by, e.g. subtraction of ballistocardiogramm from the EEG / MEG data to avoid contamination by MCG. If you want to look at further things like changes of MEG in relation to heart rate, you should try to determine the flow (and its delay, e.g. by combining ECG / echography of the heart with transcranial doppler, if feasible) to get an idea of the delays to apply in averaging time-locked activity of the brain.

Very complicated thinking, how could you for sure disentangle an electric or magnetic recording with a mechanic source or record, it just give you a time reference nothing more. And a Doppler recording doesn't give a flow, it gives a speed (the volume is not known).