Presentation patterns were quite similar for men and women with a large likelihood of Acute Coronary Syndrome (ACS) for those presenting in the morning. This may be related to changes in the thrombolytic activity, platelet aggregability and sympathetic system activation. In patients with ECG signs of ST elevation ACS, the likelihood for ACS was much smaller for men than for women. This can perhaps be explained by differences in the size of the heart, and in the anatomy and electric properties of the thorax. There may be a need for different ECG criteria for ACS for men and women.