Ionophores are a type of antibiotic that selectively depresses or inhibits the growth of certain microorganisms in the rumen. The most common ionophore antibiotics used in veterinary medicine as coccidiostatic drugs are monensin, salinomycin, narasin, and lasalocid. Inappropriate use of these therapeutic agents has resulted in animal poisoning of various species, mainly characterized by degenerative myopathy and cardiomyopathy. This study reports an outbreak of ionophore intoxication in cattle through epidemiological, clinical, laboratory, and necropsy findings. Two mixed-breed male calves with a mean age of two years, raised in an intensive system, were attended to at the Veterinary Hospital of Universidade Federal de Campina Grande, Patos, Paraiba. One week before, they had presented decreasing appetite, diarrhea, fatigue, tottering gait, and permanent recumbency. Animals were fed grass, poultry litter, whole wheat and corn. Anamnesis, epidemiological, clinical, and laboratory examinations led to a presumptive diagnosis of ionophore atibiotic toxicosis which caused cardiac failure