The utilization of transmural myocardial triacylglycerols, phospholipids and tissue free fatty acids was studied in dogs with and without left circumflex coronary artery occlusion for time intervals up to 4 hours. Results from 14C-labeling experiments reflected a continuous and dynamic turnover of transmural triacylglycerol fatty acids, phospholipid fatty acids and tissue free fatty acids in control dogs with patent coronary arteries. Coronary artery ligation resulted in markedly diminished glycerolipid utilization. However, 14C-labeled free fatty acid utilization continued in the ischemic state. No net changes in chemically determined total triacylglycerols were observed in any region through 2 hours of occlusion, but a substantial increase was observed transmurally after 4 hours. Certain mechanisms involved in the observed ischemia-induced alterations of myocardial lipid metabolism are discussed within the context of the current literature.