There are so many typo errors in the activity "Heartbeat Measurement Circuit" that it becomes confusing to read.
For instance Amplifier Circuit (C1, A1, R3), should be (C1, A1, R1).
First order low pass filter (A2, R4,C2), should be (A2, R2, C2).
Throughout the rest of the article, the resistor numbers are totally wrong.
At the final amplifier, there is no R6.
On the hardware set up picture, the OpAmp is wrong ! It should be OP484, but shows OP482.
I notice naming typos in many of the activities, but this is the first one with so many that it becomes very confusing.