Abstract Background The HACEK group of organisms are one of the infrequent causes of infective endocarditis (IE)(5% of cases in adults).Cultures require long incubation time and clinical presentation may be insidious,delaying final diagnosis.We report a case of subacute atypical presentation of native mitral valve Haemophilus parainfluenzae IE A 33 yo female with no history of cardiac disease was presented in our hospital with malaise,weakness &high fever till 39oC for at about two weeks.The patient was treated with levofloxacin and discharged. The 1st blood culture was negative.After 25 days the patient was presented with prolonged fever,neurological signs of TIA(motor aphasia and septic embolic episode of 2nd level on the right hand&foot).Physical exam normal,no cardiac murmurs. ECG:normal. Echo:TTE-mitral valve with thickened leaflet, presence of structures suggestive for vegetations (15x19 mm) at the posterior leaflet, perforation of the posterior leaflet causing an IM mild-moderate.TEE-mitral valve with small posterior leaflet, big anterior leaflet with mobile vegetations of coral-forms with diameter maximum 20x10 mm,located at A3 scallop of mitral valve at posteromedial commissural,with a perforation at this level causing moderate IM.No other pathological findings.Cranial CT scan-no data of any acute intracranial abnormality.Body CT scan-a low uptake area of the renal parenchyma related to acute pyelonephritis/infarction.Blood tests-elevated CRP & thrombocytopenia.Blood culture(2nd one): Haemophilus parainfluenzae.Treatment-The patient went on ceftriaxone and underwent a surgical mitral valve repair with mitral annuloplasty and patch placement because of the size of the vegetation and the embolic risk.We also respect the desire of the patient to be pregnant.The patient improved, no fever. Follow-up:CRP normal.TTE echo showed no evidence of the previously detected vegetation with a residual mild MR.The patient was discharged home followed up after 6 weeks with full recovery. Discussion We present the case of a young healthy woman without any diseases,admitted with the symptoms of a simple flu-like syndrome with a negative blood culture, but complicated later in one of the rarest forms of IE with Haemophilus parainfluenzae. HACEK organisms are most often associated with IE, although rare, can be extremely serious because of the tendency of big size vegetation and embolic episodes,but outcomes generally are successful if the organism is identified early and treated appropriately.The treatment of a HACEK infection is based on the location of the infection,clinical severity and available susceptibility data.According to the ESC recommendations Ceftriaxone or ampicillin/sulbactam is the therapy of choice for patients with HACEK endocarditis in both native and prosthetic-valve endocarditis.Fluoroquinolones may be considered as alternative therapy.Regardless of the agent chosen,treatment should last 4– 6 weeks,depending upon the type of valve involved Abstract P1459 Figure.