Authors describe the case of 4 years old girl with Down syndrome, who was operated due to common atrio-ventricular canal and persistent Botalli's duct. Intermittent total atrio-ventricular block (without significant bradycardia) has been observed one year later and considered as a late postoperative block requiring no treatment. Kawasaki disease was diagnosed because of the presence of 4 out of 6 leading symptoms appearing in typical chronology (fever, mouth and throat inflammation, conjunctivitis, erythema with subsequent desquamation of skin on palms and feet). ECG revealed total atrio-ventricular block, however with significant bradycardia. ECHO showed aneurysms in both coronary arteries. Standard treatment of Kawasaki disease was administered (immunoglobulins, acetylsalicylic acid) and orciprenalin due to described cardiac block. Pacemaker was implanted because of bradycardia. The literature review showed that the treatment with immunoglobulins and aspirin can reduce the risk of coronary aneurysms development. On the other hand, identification of patients at risk coronary aneurysms development is not possible on the ground of biochemical blood analysis and physical signs. Thus, all the patients stricken should be treated with described above costly drugs (immunoglobulins). Finally, the algorithm of procedures in patients with coronary aneurysms was presented.