This little book first appeared on the public stage to a small audience in 2011. The 2019 6th edition now bows out for the last time. There had to be further editions after the first when the author, his most severe critic, introduced new ideas and corrected the errors of the previous ones. But running through them all has been the strong thread of his conviction that the placental supply for the foetus feeds the left atrium, not the right, and that it is the foetus which is delivered: the baby is born after the delivery when the first deep breath is taken. In this final edition the author shows the correct supply for the left atrium by some fundamental facts of physiology and by direct observations of the foetus: human and sheep, which demolish the long-established orthodox accounts. One of his glaring errors in the 4th version was to deny the lungs a pulmonary circulation. In this present edition he not only corrects himself, but uncovers the full pathway of this circulation, which shows the course taken by the arterial supply and the venous return. There is a comprehensive valuable account of the foramen ovale, which, like many of the other aspects of this work, are entirely new. The unique characteristics of the foetal heart sounds are described, which any lady in the later months of pregnancy may hear with a Doppler monitor, and which confirm that the placental flow enters the left atrium. The invisible birth changes which have never been seen, are guessed at in full detail. The work is generously illustrated with diagrams, drawings and photos from the hands of the author.