OBJECTIVE To assess the accuracy of echocardiography with Simpson's apical biplane method in screening for left ventricular systolic dysfunction (LVSD) in patients six months after acute myocardial infarction (AMI) as compared with radionuclide ventriculography by assessing the proportion of clinically significant errors that occur with echocardiography. METHODS Comparison of results of echocardiography and radionuclide ventriculography in assessing left ventricular ejection fraction among patients six months after AMI. METHODS District general hospital. METHODS 86 patients thrombolysed for AMI at six month follow up. METHODS None. METHODS Correlation coefficients, mean differences, 95% limits of agreement, and differences of clinical significance between left ventricular ejection fraction on echocardiography and on radionuclide ventriculography. RESULTS The correlation coefficient between techniques was 0.90, mean difference 1% (p = 0.04), and 95% limits of agreement -13.0% to 10.3%. Only one patient (1.2%, 0.0% to 6.3%) was classified as having normal systolic function on one imaging modality but significant LVSD on the other. Overall accuracy between the two techniques was 86%, kappa value of agreement 0.78. CONCLUSIONS Echocardiography is a valid tool to screen for LVSD in patients six months after AMI, accurately differentiating normal from abnormal systolic function and showing excellent agreement with radionuclide ventriculography. This study supports the use of echocardiography in screening for LVSD in chronic stable patients after AMI or alternative high risk patients, with few differences of major clinical significance likely to occur.