The process of perceiving symptoms of illness is complex, and many patients delay seeking care when symptoms of acute myocardial infarction occur. However delayed treatment can have great consequences for the prognosis. This article reports on a grounded theory study, the aim of which was to increase our understanding of the individual's thoughts, feelings and actions at the onset of an acute heart attack. Qualitative analysis of semi-structured interviews revealed four different ways of perceiving the onset of symptoms: understanding, misinterpretation, amazement and disregard. The symptom perception categories were related to two core categories labelled health beliefs and acute reactions. Some persons were aware of risks for coronary heart disease and were ready to seek care immediately. Several others had illusions of invulnerability. Such illusions caused people to delay seeking care at the onset of symptoms of myocardial infarction.