SUMMARYBackground: Endocardiosis (or chronic valvular heart disease, CVHD) is the most common disease of the heart in dogs. Due to its frequent occurrence, the significance of this disease is large in pet veterinary practice.Objectives: we have been looking for answers to the questions relating to the endocardiosis of dogs. We aimed to find out at what stage this disease was typically determined and in what percentage of the cases we experience deterioration in the condition of the animal. Materials and methods: Using a retrospective data analysis, we examined a 7 years period and checked the data of 566 dogs suffering from endocardiosis (CVHD). In every dog echocardiogarphy was performed to determine the diagnosis of CVHD. Staging of the disease was based on the classification system of the American College of Cardiology/American Heart AssociationResults and discussion: we found that most of the patients (45.2%) only showed the subtlest lesions characteristic of the disease; these were the stage B1 patients. In the case of 193 individuals, during the period several heart ultra-sound examinations were performed as well. In 70% of these patients (135 indi-viduals) where multiple examinations had been carried out, we found that there had been no deterioration in the condition of the animal. Those dogs which were in B1 stage group at their first examination, have a 79% chance of not developing the signs of heart failure. The time of progress in every group was more than 1 year. Examining the stage deterioration, we found that age correlated signif-icantly negatively with the time between stage deterioration. This means that the endocardiosis in older dogs progress faster both from stage B1 into B2 and both from stage B2 into C. In 53 cases, we could follow the fate of the animals until they died. Out of these, death or euthanasia occurred because of heart disease in 28 cases, while the animals died or were put to sleep for other rea-sons in the remaining 25 cases. Comparing these two groups we found a high proportion of males (87%) among those who died of CVHD.