Sparkfun Electronics AD8232 Hook-Up Manual page 10

Make sure the RA and LA sensor pads are on correct sides of the heart.
Try not to move too much while taking a measurement.
Try to use fresh pads for each measurement. The pads loose the ability to pass signals with multiple applications.
Prep and clean the area you plan to stick pads. This will help make a good connection (hair is not a good conductor).
You may have to adjust sensor placement for different individuals.
If the sensor pads are not placed correctly on the body or the cable is not connected, you may see an output similar to the image below in the serial monitor. The
values will either clip the waveform between 0 and 1023 or display an "!".
As a result, you will either see a flat line in the Arduino serial plotter or nothing will be drawn in the Processing's display window. If this happens, you'll need to
check your solder joints and try placing the sensor pads to a different location around the body.
Arduino Serial Plotter
If you happen to moving a lot or flex your muscle, you will not get a distinct waveform. Make sure to remain still and relax as the sensor is taking measurements.
You may see a few distinct waveforms but it will not be as reliable.
Arduino Serial Plotter
Displaying a Noisy Waveform
Depending on where the sensor pads are placed, you may still get a distinct waveform similar to the graphs displayed in the Arduino serial plotter below. You
may notice the QT interval pulsing even though the center value is noisy. This is not as desirable as the waveforms shown earlier and the pads may need to be
moved to a different location depending on your application. When inspecting the graph on the right further, you'll notice that there is a gradual spike at the end of
the waveform. This was due to the sensor picking up movements from a user breathing deeply similar to when a user is moving a lot or flexing a muscle. If this
happens, make sure to not force the breathing.
Displaying Flat Line
Processing Sketch
Displaying a Noisy Waveform
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Processing Sketch
Displaying Nothing