A study of vital statistics data from five Minneapolis-St. Paul winters indicates cardiovascular mortality is influenced by winter temperatures and snow. Although air temperature was not statistically implicated in triggering cardiovascular mortality in four of the five study winters, during the winter of 1976-77, about 15 per cent of the variance in daily cardiovascular mortality could be attributed to fluctuations in the daily minimum air temperature. Snow influenced mortality on the day of occurrence as well as the two days following a snowfall. There appear to be some differences in the ability of winter weather to influence mortality from acute myocardial infarction (ICD 410) and old myocardial infarction (ICD 412). The variance in daily ICD 410 mortality attributable to the influence of snow is somewhat less than that in daily ICD 412 mortality. The greatest variance in daily ICD 412 mortality that could be ascribed to snow occurred during the winter of 1974-75, and was 13 per cent. It is likely that rain intermixed with snow may also trigger increased mortality from cardiovascular disease. A combination of rain and snow can produce dramatic increased in mortality from ICD 410. Study of mortality data from five winters indicates that snow is somewhat more important in triggering deaths from heart disease than is air temperature.