Objectives: To develop an adult guinea pig model of lipotoxicity and explore the underlying mechanisms associated with changes in the expression of the delayed rectifier potassium current (I-K). Background: Lipotoxicity may represent a common link among metabolic disorders and a higher vulnerability to arrhythmias. Methods: Whole-cell patch clamp, and palmitic acid (PA, a potent inducer of lipotoxicity), were used to assess mechanisms of short-term (similar to 50 days) high-fat diet (HFD) feeding on atrial electrophysiology in guinea pig hearts and myocytes. Results: HFD fed guinea pigs were significantly heavier, displayed hypertriglyceridemia and hypercholesterolemia; but no signs of hyperglycemia or inflammation compared to low-fat diet fed controls. Increasing cardiac PA levels, resulted in shortened atrial action potential duration, and increased I-K density. Inhibition of phosphoinositide 3-kinase (PI3K) prevented increases in I-K due to PA. Acute (>= 1hr) exposure of atrial myocytes to exogenous PA (1 mM) increased the density of the rapid delayed rectifier potassium current I-Kr, while it was decreased with the unsaturated oleic acid (OA, 1 mM). Serine-threonine protein phosphatase-2 (PP2A) inhibition with cantharidin reversed the effect of OA on I-Kr. Conclusion: Our data provide evidence of a novel lipotoxic guinea pig model with signs of vulnerability to arrhythmias. Inhibition of PA/PI3K/I-K and/or activation of the OA/PP2A/I-Kr, pathways may be therapeutically beneficial for lipotoxic arrhythmias. (C) 2019 The Author. Published by Elsevier Inc.