Abstract: Abstract   Objective   The purpose of this study was to determine whether a time variation could be observed in the occurance of acute myocardial infarction (AMI) in older patients in nearly three years. Methods    A retrospective analysis of patients diagnosed with AMI between 2009 and 2012 in the department of Cardiology of The Second Hospital of Tianjin Medical University (n=908 patients) was carried out. We calculated the number of AMI cases day by day. Combined with the general clinical data ,we analysis that whether a seasonal or monthly or weekly variation could be observed in the occurance of AMI in the elderly .Results    The occurance of AMI in older people increases year by year（p＜0.01）.A peak period of the incidence of AMI was recorded during winter, while minimum number of events were found during summer. Significant difference was observed between the number of events each season (p＜0.01).And the monthly occurrence of AMI was highest in January and lowest in June (p＜0.05). But the variation was only found in the patients which had coronary heart disease history or ST segment elevated in ECG or had poor heart function (P＜0.05). The cicadian rhythm of AMI morbidity was found, and the rhythm has no relation with seasons and months (p＜0.01) . The time peak period of AMI morbidity was found in the morning. Conclusion   Results of our study reveal that the incidence of AMI is on rise year by year and shows a characteristic rhythm with respect to seasons and months .Based on the results ,we can formulate prevention measures.

Key words: acute myocardiac infarction, acute disease, morbidity, season rhythm, monthly variation, cicadian rhythm, seasonal variation, 老年人