Atrial natriuretic peptide is a circulating hormone secreted by the atrial myocytes of the heart. It is released in response to increased atrial pressure,' which is generally equal to increased stretch and dilatation of the atrial wall. Plasma atrial natriuretic peptide rose during exercise.2The term "athelete's heart" was introduced byHenschen in 1899.' In this condition all the chambers of the heart are dilated and there is hypertrophy of the myocardium due to physical training.4"The purpose of this study was to determine whether the hypertrophy and dilatation of the heart seen in well trained persons influence the plasma concentration of atrial natriuretic peptide at rest or during exercise.Requests for reprints to Dr Jens Svanegaard, Departnent of Cardiology, Odense University Hospital, Odense C, Denmark DK-5000.Accepteq for publication 27 June 1989 Patients and methods We studied six male footballers who trained strenuously and six normally active healthy matched controls (aged 21-30 years). None was taking medical treatment. The controls did not participate in any form of athletics for more than four hours a week. They all gave informed consent and the study was approved by the local ethics commnittee.All of the investigations were undertaken between 3 pm and 7 pm. Echocardiography, with cross sectional and M mode recordings, was performed with a Hewlett Packard 77020A ultrasonograph and a 3-5 MHz transducer on men in the supine position.All the M mode measurements originated from three or four consecutive cardiac cycles graded according to the system of the American Society of Echocardiography.