OBJECTIVE: This study was done to evaluate the degree of change in autonomic activity, manifested as heart rate variability (HRV), from acute phase of MI to convalescent period of AMI. DESIGN: Single center, observational prospective study. PLACE AND DURATION OF STUDY: Department of Cardiology, Shaikh Zayed Hospital, Lahore. The study was completed in one year from June 2000 to July 2001. SUBJECTS AND METHODS: Thirty consecutive patients presenting within 24 hours of an ST segment elevation AMI with or without thrombolysis were included. First 24 hour Holter recording was done within 24-36 hours after AMI and the second was done before discharge. RESULTS: The mean hospital stay was 7.07 +/- 2.56 days. Mean duration between the two recordings was 5.47 +/- 2.36 days. The mean standard deviation of normal sinus interval (SDNN) was 65.07 +/- 25.11msec & 63-97 +/- 23.38msec; mean standard deviation of averaged sinus beats for 5 minutes segments of entire recording (SDANN) was 51.27 +/- 18.57msec and 55.83 +/- 19.65msec and mean SDDN index was 34.57 +/- 17.15msec and 30.57 +/- 14.89msec during early phase of acute MI & pre-discharge recordings respectively. There was no statistically significant difference in HRV between early phase of acute myocardial infarction and of pre-discharge recordings. CONCLUSION: HRV may be monitored for risk stratification at any time post AMI prior to discharge.