I found a little heart rate sensor @ ICstation. It is a clone of the open hardware pulse sensor. The sensor is well documented, and it comes with Arduino and Processing example code.
To try it out I connected the sensor to an ATmega328 running at 3.3V and loaded the example Arduino code. I could now see my heart beat on the Arduino serial monitor
Make a robot friend with Adafruit’s CRICKIT – A Creative Robotics & Interactive Construction Kit. It’s an add-on to our popular Circuit Playground Express, FEATHER and other platforms to make and program robots with CircuitPython, MakeCode, and Arduino. Start controlling motors, servos, solenoids. You also get signal pins, capacitive touch sensors, a NeoPixel driver and amplified speaker output. It complements & extends your boards so you can still use all the goodies on the microcontroller, now you have a robotics playground as well.