Frequency domain representation of a short-term heart-rate time series (HRTS) signal is a popular method for evaluating the cardiovascular control system. The spectral parameters, viz. percentage power in low frequency band (%PLF), percentage power in high frequency band (%PHF), power ratio of low frequency to high frequency (PRLH), peak power ratio of low frequency to high frequency (PPRLH) and total power (TP) are extrapolated from the averaged power spectrum of twenty-five healthy subjects, and 16 acute anterior-wall and nine acute inferior-wall myocardial infarction (MI) patients. It is observed that parasympathetic activity predominates in healthy subjects. From this observation we conclude that during acute myocardial infarction, the anterior wall MI has stimulated sympathetic activity, while the acute inferior wall MI has stimulated parasympathetic activity. Results obtained from ARMA-based analysis of heart-rate time series signals are capable of complementing the clinical examination results.