Early transthoracic echocardiography has useful prognostic value in left-sided native valve endocarditis despite limited diagnostic performance, Abstract To investigate the prognostic implications of findings on early transthoracic echocardiography (TTE) in patients with definite left-sided native valve infective endocarditis (LNVIE). We reviewed a 10-year retrospective cohort of consecutive patients with definite LNVIE treated at a tertiary cardiothoracic centre. TTE studies performed within the first seven days of the index blood culture (for culture-positive cases) or hospital admission (for culture-negative cases) were reviewed for the presence of valvular vegetations, perivalvular abscesses, aortic or mitral regurgitation of moderate or greater severity or a bicuspid aortic valve. Six-week outcomes included all-cause mortality, cardiac surgery for endocarditis or new embolic cerebral infarction. Early TTE was performed in 118 of 151 episodes of definite LNVIE at a median of two days after the index blood culture or hospital admission. Findings on these studies included valvular vegetations or abscesses in 74 patients, moderate or severe aortic or mitral regurgitation in 67 patients and a bicuspid aortic valve in 19 patients. The presence of any of these findings conferred a relative risk of any adverse six-week outcome of 4.80 (95% confidence interval 1.6–17, p = 0.001). The presence of a bicuspid aortic valve appeared particularly predictive of the need for cardiac surgery, including for clinically occult paravalvular abscesses. Early TTE can be used to stratify patients with LNVIE by the risk of major endocarditis-related adverse outcomes occurring within the first six weeks of treatment.