Female pigs, fed diets in which 42% of the caloric intake came from either rapeseed oil, fish oil, partially hydrogenated fish oil, partially hydrogenated soybean oil or lard, were killed after one week, five weeks, six months and one year. Type of fat or length of feeding did not affect the cardiac content of total fat which was normal in all animals. The fatty acid pattern of tissue triglycerides only partly reflected the fatty acid pattern of diets. The relative amounts of C22:1 and C20:1 were greatest after six months and levelled off during the following six months. The content of C22:1 in cardiac triglycerides never exceeded one fifth of the dietary concentration. Microscopic lipidosis was found in some pigs after one week, five weeks and six months. Minor heart lesions consisting of focal necrosis of muscle cells were found after one week and more frequently after six months and one year. No relationship between incidence and severity of the heart lesions and any particular type of fat in the diet could be found.