In 73 patients with acute occlusion of single coronary artery, the authors assessed the possibilities of ECG and echocardiography in determining non-invasively which of the 3 main arteries had been occluded. The sensitivity of ECG for the individual arteries and particular ECG signs ranged between 30-98%, the specificity was between 86-100%. While it was always possible to determine occlusion of the left anterior descending coronary artery (LAD), in several cases it was difficult to distinguish between occlusion of the left circumflex (LCX) and the right coronary artery (RCA). The LCX occlusion is a frequent source of error in interpreting electrocardiograms of patients with fresh myocardial infarction. The sensitivity of echocardiography in identifying the occluded coronary artery ranged between 77-100%, specificity 97-100%. The following ECG and echocardiographic signs of coronary occlusion were determined. The LAD occlusion is indicated by ECG changes in V1-4, and anteroseptal and apica asynergy on echocardiography. LCX occlusion: increased R wave amplitude in V1, and lateral and posterior wall asynergy. The RCA occlusion: ECG changes in II, III, aVF, asynergy of the posterior wall and part of the septum and right ventricle. These combined signs make possible the identification the occluded coronary artery in 95% of patients with myocardial infarction.