['The present study aimed to confirm the existence of a circadian pattern in the onset of acute pulmonary edema (APE) and to verify whether sex, age, preexisting diseases, and clinical causes determining the event may influence it.', 'The study considered all consecutive cases of APE observed at the St. Anna General Hospital of Ferrara, Italy, during a 7-year period from January 1, 1992, to December 31, 1998. The sample population was divided into subgroups by sex, age (<75 and > or =75 years), presence or absence of diabetes and hypertension, clinical causes determining the event (i.e., acute myocardial infarction (AMI), pulmonary embolism, arrhythmias). The most important associated or concomitant diseases were also considered (i.e., coronary heart disease and angina, previous myocardial infarction, chronic cardiac failure, dilatative cardiopathy, chronic atrial fibrillation, valvular disease, chronic obstructive pulmonary disease, chronic cor pulmonale, malignancy, chronic renal failure). Time of symptom onset of each event was recorded accurately, then tabulated into 24 increments of 1h (e.g., 06:00 to 06:59 was reported as 6 A.M.). For statistical chronobiological analysis, partial Fourier series were used.', 'During the 7-year period, 1321 consecutive cases of APE in 1014 different subjects were observed. The majority of events occurred at night, and statistical analysis showed a 24h rhythmicity both in the total sample population and in all considered subgroups, with the only exception being patients with pulmonary embolism and arrhythmias, for which the small number of cases made the study of rhythms in APE impossible.'] Is circadian variation in onset of acute cardiogenic pulmonary edema independent of patients ' features and underlying pathophysiological causes?