In order to assess the short-term reproducibility of the most important ergometric parameters, 108 males (mean age 50.3 ± 7.8 years) underwent a functional stress test (FST) on average 35 days after myocardial infarction. The exercise test was repeated 3 days later in the same conditions. Patients were fasting and in pharmacological washout. The following parameters were analyzed: total work performed (TWP), VO<sub>2</sub>, heart rate (HR), systolic blood pressure (SBP), arrhythmias and S-T segment depression and elevation. TWP and VO<sub>2</sub> values did not show any significant difference during the two tests under the various workloads. HR and SBP responses proved to be well reproducible in patients with HR and SBP not exceeding the mean values obtained from 222 normal subjects who underwent the same exercise test by more than ± 1 SD; reproducibility was significantly lower in the other patients, particularly in patients with HR and SBP exceeding normal values by more than ± 1 SD. Therefore, in this case, further FST are necessary to obtain more reliable parameters to decide on individual pharmacological and exercise prescriptions. Arrhythmias were reproducible up to 67% (p < 0.01) regardless of Lown’s class and the presence of S-T segment depression or elevation. S-T segment depression or elevation was reproducible up to 100%.