Electrocardiography for Cheap: DIY ECG Uses One LM741 Op-Amp, Five Resistors, and 'Penny Electrodes' « Adafruit Industries – Makers, hackers, artists, designers and engineers!
DIY ECG using a Analog Discovery 2 and LabVIEW - Hackster.io
AD8232 ECG Module with Arduino – Heart Rate Monitor
AD8232 Diy Kit forArduino ECG Physiological Measurement Heart Pulse ECG Monitor Sensor Module Single Lead Heart Rate Monitor - AliExpress
DIY EKG Using Arduino and Javascript - EEWeb
Build Your Own ECG-EKG Unit | Nuts & Volts Magazine
DIY ECG with 1 op-amp
The Do-It-Yourself Electrocardiogram | Biomedical Engineering Education