An analysis of the relationship between the sudden changes in weather and the onset of cases of acute myocardial infarction was made in three Dallas hospitals, comprising a series of 1,386 patients admitted during a five-year period from 1946 to 1951. An increased frequency of occurrence of acute myocardial infarction was noted during periods of sudden inflows of polar and of tropical air masses. It appears from the present study that sudden meteorologic changes exert an adverse effect on patients with coronary artery disease.