I worked in cardiology, so this was a delightful read; exhilarating, in fact. Very technical, but extremely well written and informative. It's old, but always applicable, even though electrophysiology has advanced a great deal since it was written. I particularly appreciated the insistence that we work to understand the electrophysiological causes of ECG variations. Reading ECGs is actually the work of a detective-like mind - you have to understand that what you see on the paper is evidence of what is happening in the heart, and never forget that your interpretation could be incorrect.