Background: The efficacy of interventions in ST-segment elevation myocardial infarction (STEMI) assessed by a decrease in inpatient mortality in Poland is very high. However, a rise in mortality rate is recorded within 3 years of the discharge from the intervention centre. In order to reduce out-of-hospital mortality, the treatment should be continued with cardiac rehabilitation after hospitalization. The aim of this retrospective study was to evaluate the effect of cardiac rehabilitation on exercise capacity increase patients with STEMI with regard to their age, gender, Body Mass Index (BMI), ejection fraction (EF), concomitant diabetes and nicotine dependence. The effectiveness of cardiac rehabilitation was assessed by exercise ECG (electrocardiogram) stress test or the 6-min walk test, prior to and after cardiac rehabilitation completion. Methods: The study group included 100 randomly selected patients undergoing cardiac rehabilitation after STEMI, aged 40–75 years, with BMI ≤ 40 kg/m2, with controlled arterial hypertension, without anemia and any pulmonary comorbidities. Results: The study patients’ exercise capacity was observed to have increased significantly (+1 metabolic equivalent (MET) in exercise ECG stress test and +75.4 m in the 6-min walk test) regardless of their gender, age, BMI and nicotine dependence. Conclusions: This study proved that every patient with STEMI could benefit from cardiac rehabilitation. Nicotine-dependents, males, patients aged ≤55 and those with reduced EF (<50%) were found to have benefitted most substantially.