The endocannabinoid system (ECS), modulated by metabolites of linoleic acid (LA), is important in regulating cardiovascular function. In pregnancy, LA is vital for foetal development. We investigated the effects of elevated LA in H9c2 cardiomyoblasts in vitro and of a high linoleic acid (HLA, 6.21%) or low linoleic acid (LLA, 1.44%) diet during pregnancy in maternal and offspring hearts. H9c2 cell viability was reduced following LA exposure at concentrations between 300 and 1000 µM. HLA diet decreased cannabinoid receptor type 2 (CB2) mRNA expression in foetal hearts from both sexes. However, HLA diet increased CB2 expression in maternal hearts. The mRNA expression of fatty acid amide hydrolase (FAAH) in foetal hearts was higher in females than in males irrespective of diet and N-acyl phosphatidylethanolamine-specific phospholipase D (NAPE-PLD) mRNA expression showed an interaction between diet and sex. Data indicate that a high LA diet alters cell viability and CB2 expression, potentially influencing cardiac function during pregnancy and development of the offspring’s heart.