The possibility of early prediction of acute myocardial infarction (AMI) was assessed in 7,157 consecutive patients coming to our emergency room during a 21-month period with chest pain or other symptoms suggestive of AMI. Of these patients 921 developed an AMI during the first 3 days in the hospital. Of the 4,690 patients admitted to hospital, 1,576 (34%) had a normal admission electrocardiogram, and 90 of these (6%) developed AMI. Of 1,964 patients with an abnormal electrocardiogram without signs of acute ischemia (42% of those admitted), 268 (14%) developed AMI, and 563 (51%) of 1,109 patients with acute ischemia on the electrocardiogram (24%) developed AMI. All patients were prospectively classified in the emergency room on the basis of history, clinical examination and electrocardiogram into 1 of 4 categories, according to the initial degree of suspicion of AMI. Of 279 admitted patients judged to have an obvious AMI (6% of the 4,690), 245 (88%) actually developed AMI; of 1,426 with a strong suspicion of AMI (30%), 478 (34%) developed one; of 2,519 with a vague suspicion of AMI (54%), 192 (8%) developed one; and of 466 with no suspicion of AMI (10%), 6 (1%) developed one. Thus, only a low percentage of the patients with a normal initial electrocardiogram or a vague initial suspicion of AMI developed a confirmed AMI.