Dental prophylaxis is a key component of prevention and treatment of oral diseases in dogs, combining diagnostic, therapeutic, and preventive procedures. Preoperative clinical examination often reveals incidental findings - asymptomatic pathologies capable of significantly affecting the course of anesthesia and the outcome of surgical intervention. The objective of this study was to evaluate the hemodynamic effects of idiopathic pericarditis during dental prophylaxis under general anesthesia. In all animals, preoperative echocardiography revealed free fluid in the pericardial cavity with a thickness of 3-5 mm without signs of cardiac tamponade. Patients were divided into two groups: Group 1 (n=3) - dogs that underwent pericardiocentesis with complete fluid drainage before dental prophylaxis; Group 2 (n=3) - dogs with a small fluid layer left (1-2 mm). Hemodynamic parameters were monitored during anesthesia and dental sanitation. Histopathological examination of pericardial tissue samples obtained over the year confirmed the diagnosis of idiopathic pericarditis. Group 1 demonstrated stable hemodynamic parameters during the procedure: systolic blood pressure 95-110 mmHg, heart rate 65-80 bpm. All patients had no hypotensive episodes, and the rhythm was regular. Group 2 was characterized by a significant decrease in hemodynamic parameters: systolic blood pressure 72-85 mmHg, heart rate 48-58 bpm. Histopathological examination of all samples revealed lymphocytic-plasmacytic inflammation without signs of infection or neoplastic changes, confirming the diagnosis of idiopathic pericarditis. Even a small volume of pericardial effusion (3-5 mm) can have a significant impact on hemodynamics during anesthesia when performing surgical procedures. Complete drainage of pericardial fluid before dental prophylaxis ensures hemodynamic stability and anesthetic safety in dogs with idiopathic pericarditis.