A 15-year-old boy was admitted to the emergency department with arthralgia of the knee. He was diagnosed with acute rheumatic fever based on clinical examination, electrocardiography, echocardiography, and elevated inflammatory markers including C-reactive protein, erythrocyte sedimentation rate, and anti-streptolysin O titre. First-degree and second-degree Mobitz type 1 atrioventricular blocks, moderate frequency uniform ventricular premature beats, as well as non-sustained ventricular tachycardia, were detected on 24-hour Holter electrocardiography monitoring.

We report a case of severe Kawasaki disease with giant coronary artery aneurysms, multiple systemic arterial aneurysms, and delayed-onset, independently progressive bivalvular insufficiency due to direct valvulitis. Despite controlled inflammation and favourable coronary evolution under immunosuppressive therapy, the patient required surgical valve repair. This case highlights the unpredictable nature of complex Kawasaki disease phenotypes and underscores the need for comprehensive vascular imaging and lifelong follow-up, as atypical features may lead to independent complications.