We recently encountered a 49-year-old female who developed fever due to group A streptococcal (GAS) bacteriaemia spreading to an abscess in the iliac muscle and a bacterial monarthritis of the right knee with a sterile arthritis of her left knee. Treatment was started with a six-week course of intravenous penicillin. She developed a mitral valve insufficiency and pericarditis on the tenth day of admission. In the third week heart failure developed with, on echocardiograph, a high output left ventricular failure without signs of valvulitis or myocarditis. Using a diuretic regimen she was recompensated. Because of the pericarditis with mitral valve insufficiency corticosteroids were given, which had a rapid beneficial effect. A discussion follows on the position of acute rheumatic fever versus post-streptococcal reactive arthritis in this clinical picture and the literature is updated.