Regarding the study of EKG, it is the topic of Heart Block that appears to confuse most persons. Let's take a look at it:

Demystifying the EKG

At work I ponder images
The waveforms of an EKG,
In the language of the beating heart
It usually is clear to me,
But sometimes I am mystified
About the A.V. block,
It manifests so many ways
My brain goes into shock.

First degree or second degree
Third degree and more,
P-waves are advancing
And can't get through the door,
I must utilize some rules
As my analyzing key,
To unlock the great unknown
Of this crazy EKG.

Fibril_late; 1997