Clarification of the cyclic pattern of emergency events is useful for identifying risk factors for emergency events. We attempted to characterize the circadian variation in emergency calls for the elderly (aged 65 years or older) because the use of emergency transportation by elderly patients is increasing rapidly. The study targeted mainly patients with cardiovascular disease. Additionally, the study analyzed circadian variability in the occurrence of cardiopulmonary arrest (CPA) and heat stroke. Data for this study were obtained from computerized records of ambulance transport from 1997 to 2003 (a total of 874,495 transported patients) managed by the Emergency Medical Division of the Yokohama Fire Bureau. A partial Fourier model was used to analyze circadian patterns of emergency calls for each disease category and determine the peak time of occurrence of disease events. A prominent peak of cardiovascular disease and CPA in the morning was observed among elderly patients, whereas amplitudes of the morning and evening peaks were almost the same among younger patients. Heat stroke among elderly patients occurred frequently from 10:00 AM to 3:00 PM, and the occurrence peaked around noon. The increase in cardiovascular disease events and CPA during the morning among elderly patients may be due to a natural fluctuation in blood pressure. A morning increase in hemoconcentration induced by dehydration during the night is thought to be another cause of the frequent occurrence of cardiovascular disease, CPA, and heat stroke events in the morning hours. In conclusion, there was a prominent peak in the morning in the occurrence of emergency events such as cardiovascular disease, CPA, and heat stroke events among the elderly.