The following is the circuit you will have to build.
For the code you will have to load a filter library.
https://github.com/JonHub/Filters
Download the zip file and place it in your arduino libraries folder.
When in the arduino program go to the menu Sketch>Include Library>Add .ZIP Library
Here is the following code you need for your sensor to work.
Upload the program and open the plotter in the Tools menu. Try different fingers between the IR LED and IR Sensor to see what works best for you.
Here are some visuals that you might see that would represent your heart beat.
If you are not getting a consistent frequency you have noise and might be moving or talking too much. Also, check if your circuit is built correctly.
Visit a student's post for more about the experimentation they did to make the arduino plot out their heart signal.
http://avatanstem.blogspot.com/2016/02/heart-rate-monitor-part-1.html