Summary.Eight dogs treated for from 8 to 20 months with cod liver oil in a dose 0.1‐l‐(5) cc. of oil per kg. bodyweight per day, show obvious alterations of their electrocardiogram and degenerative heart lesions of the usual type.As may be expected from the comparatively small dose of oil, the alterations of the Ecg. are rather small, mainly consisting of alterations in the size and direction of the T‐summit and prolongations of the times of the curve. Clear changes of these kinds occur in all the cases and are rather uniform. Curves such as those occurring in bundle branch block are indicated only in two cases, one of which received the greatest dose of oil administered.There is certain evidence that even so small a dose as 0.1 cc. of oil per kg. bodyweight per day is injurious to the heart of the dog.The alterations of the Ecg. may occur within 2–4 months after the commencement of the tr