OBJECTIVE: To examine the process by which patients with acute myocardial infarction recognize illness and the need for medical treatment. DESIGN: Descriptive, exploratory, qualitative. SETTING: The coronary care and progressive care units of two midwestern medical centers. SUBJECTS: Thirty men and women with a diagnosis of acute myocardial infarction. METHODS: Open-ended interviews were conducted on the fourth or fifth day of hospitalization. All interviews were recorded on audiotape and transcribed. Data were analyzed by using grounded theory methods. RESULTS: Findings of the study indicated that determining illness and the need for medical attention was often a difficult process involving phases. The first phase involved attending to or ignoring bodily sensations as they come and go or additional sensations develop. Some subjects moved precipitously to seeking treatment; others took days to attend to bodily sensations. The second phase involved comparing sensations with those from a previously experienced illness or with the subject's concept of sensations likely to accompany common ailments such as indigestion or flu or more serious illnesses such as ulcer, gallbladder disease, or heart attack. The quality of sensations experienced had an important influence on assigning probable cause and deciding that medical attention is warranted. CONCLUSIONS: The disruptive nature of signs and symptoms and how closely signs and symptoms matched the subject's prototype for a heart attack greatly influenced the determination that illness was present and healthcare was needed. These findings have implications for educating the public about the complex and variable manifestations of a heart attack.