Although the original authors, Berne and Levy, have now sadly passed away, their legacy textbook lives on, updated by Bruce Koeppen and Bruce Stanton. Compared with the 5th edition, the 6th has much better colour diagrams and has been simplified in places. A little of the detail, particularly mathematical detail, appears to have been lost in places, but overall the text remains a heavyweight in the fundamental physiology field.
I still use this book as a first source when preparing undergraduate lectures in physiology.