One hundred patients admitted to a coronary care unit with acute myocardial infarction were interviewed from a structured questionnaire to evaluate the incidence and significance of prodromal symptoms. Prodromata occurred in 65% of the subjects; this is the highest incidence ever recorded. Chest pain was the most common symptom. Characteristically it was recurrent and progressive. Patients with prodromata in contrast to those without warning are more likely to have an anterior or anterolateral infarction and the damage is more likely to be nontransmural than transmural. Prodromata have a striking relationship to pre-existing angina. Patients with angina rarely are hospitalized for acute infarction without warning. Emotional stress was not correlated with the definitive attack of cardiac infarction but was associated with the development of prodromata in some patients. These observations suggest that acute myocardial infarction is usually the culmination of a dynamic pre-coronary process.