OBJECTIVE--To determine whether the interval between the onset of symptoms of acute myocardial infarction and the patient's call for medical assistance (patient delay) is related to left ventricular function at the time of presentation. DESIGN--Prospective observational study. SETTING--Coronary care unit of Aberdeen Royal Infirmary. PATIENTS--93 consecutive patients with acute myocardial infarction. MAIN OUTCOME MEASURES--Left ventricular stroke distance, expressed as a percentage of the age predicted normal value, measured first on admission, and then daily for 10 days or until discharge. Patients were questioned at admission to determine the time of onset of symptoms and the time of their call for medical assistance. RESULTS--Median (range) patient delay was 30 (1-360) min. Mean (SD) stroke distance on admission was 70(18)%, rising to 77(19)% on the second recording, and to 84(18)% on the day of discharge. Linear regression of log(e)(patient delay) against first, second, and last measurements of stroke distance gave correlation coefficients of 0.28 (P < 0.01), 0.18 (not significant), and 0.11 (not significant), respectively. CONCLUSIONS--Patient delay within the first 4 h after the onset of symptoms of acute myocardial infarction is positively related to left ventricular function on admission. A possible explanation is that deteriorating left ventricular function influences the patient's decision to call for help. This tendency for patients with more severe infarction to call for help sooner is an added reason for giving thrombolytic treatment at the first opportunity: those who call early have most to gain from prompt management.