Introduction: Traumatic reticulopericarditis (TRP) is a severe condition in cattle caused by foreign body penetration, leading to pericardial inflammation, resulting in significant economic and welfare concerns in dairy farms. The present study aimed to indicate a case of TRP in a Holstein dairy cow, highlighting sonographic and electrocardiographic findings. Case report: A 7-year-old Holstein cow, 40 days postpartum, was referred to the large animal clinic at the School of Veterinary Medicine, Shiraz University, Iran. The cow exhibited several concerning signs, including anorexia, a significant decrease in milk yield (from 40 liters to 5 liters), tachycardia, hypothermia, reduced ruminal motility, loose feces, distended jugular veins, muffled heart sounds, and brisket edema. Sonography revealed pericardial effusion, fibrin strands, ventricular compression, and pleural effusion. Electrocardiography (ECG) indicated ST-segment elevation, PR-segment depression, and reduced QRS amplitude. Laboratory findings revealed leukocytosis (24.8 × 10³/µL), elevated liver enzymes, including aspartate aminotransferase (AST, 93.5 U/L) and alkaline phosphatase (ALP, 205 U/L), as well as hypoalbuminemia (1.95 g/dL). Based on clinical examinations, sonography, electrocardiography (ECG), and laboratory results, the diagnosis was TRP. Given the poor prognosis, culling was advised. The diagnosis was confirmed after the culling process at the slaughterhouse. Conclusion: Ultrasonography and ECG were crucial in diagnosing TRP, identifying pericardial effusion, and assessing cardiac dysfunction. Early detection of TRP in cattle with these modalities may facilitate the development of improved treatment options.