I am a fan of John R Hampton's.books. Unfortunately the ECGs in thus kindle version do not enlarge well. You should be able to expand them to fill the page, to almost real paper size. In this version the ECGs are very pixelated and unpleasant to read.
Simply a wonderfully written book. It explains complicated issues with sublime simplicity. I often take a long time to read such books but I finished this in 3 days. I recommend this as your first buy, and it may well remain your last.