Objective To observe the heart rate variability (HRV) at admission and before treatment in patients with myocardial infarction. Methods Electrocardiograms were recorded from healthy people, patients with coronary heart disease, patients with acute myocardial infarction and acute experimental ischemia animals, and shorttime HRV analysis was performed. Results Except for the heart rate, the other indexes of HRV in patients with acute myocardial infarction were significantly higher than those in healthy people, and SDNN (standard deviation of normal to normal RR intervals, representative of sympathetic tone), SD of delta NN (standard deviation of successive differences between adjacent normal cycles), NN50 (the percent of time that the difference between adjacent normal RR intervals was greater than 50 ms) and minor axis of poincare plot (SD1) which stood for parasympathetic tone, increased by 1.8, 2.7, 7.5 and 3.1 times respectively compared with healthy people. Those changes were also observed in the animal model with acute myocardial ischemia evoked by hypophysin. In comparison with healthy people, the HRV indexes of patients with coronary heart disease decreased substantially, although SDNN and SD of delta NN did not change significantly （P>0.05）, SD1 decreased significantly (P<0.01). Conclusion HRV indexes in patients with acute myocardial infarction would elevate significantly. Compared with healthy people, on the other hand, the patients with chronic coronary heart disease exhibit decreased HRV indexes. In all probability, SD1 is more useful in evaluation of the changes in autonomic nervous activities than the other HRV indexes.