- Previous studies have documented an increased incidence of cardiac mortality and sudden death during winter months. To evaluate seasonal variation in sudden death in a hot climate such as the desert region of southern Israel. We analyzed the files of 243 consecutive patients treated for out-of-hospital sudden death by the Beer Sheva Mobile Intensive Care Unit during 1989-90. Daily, monthly and seasonal incidence of sudden death was correlated with meteorological data, including temperature, heat stress, relative humidity and barometric pressure. The seasonal distribution of sudden death was 23% in spring, 21% in summer, 25% in autumn and 31% in winter (not significant). In patients with known heart disease there were more episodes of sudden death in cold weather (< 15.4 degrees C) than hot (> 34.2 degrees C) (16 vs. 3, P < 0.05). Resuscitation was less successful in cold compared with hot weather (28 vs. 11, P < 0.05). Of patients older than 65 years, 11 sustained sudden death when heat stress was below 12.4 degrees C compared to 2 patients when heat stress was above 27.5 degrees C (P = 0.05). Despite the warm desert climate, there were more cases of sudden death in older patients and in those with known heart disease during the winter season and on particularly cold days.