Introduction: Mitochondrial biogenesis is affected by peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) and can be induced through physical exercise. Lactate from the skeletal muscle produced in the heart during exercise can be used as an energy source through conversion by lactate dehydrogenase B (LDH B). This study compared the effects of continuous training (CT) and interval training (IT) on PGC-1α and LDH B levels in the adult rat hearts. Materials and Methods: Fifteen male adult Wistar rats (12 months old) were randomly divided into three groups as follows: A control Group (c), a CT group and an IT group. Training was conducted using a rodent treadmill, 5 days/week for 8 weeks. The duration was 50 min for the CT group. In the IT group, training consisted of 4 bouts of 4 min of exercise, followed by rest intervals of 1 min. Speed was increased each week. After 8 weeks of training, the rats were sacrificed, and the levels of PGC-1α and LDH B in heart tissue were measured using enzyme-linked immunosorbent assay. Results: Differences in PGC-1α levels between groups were statistically significant (P = 0.008), while differences in LDH B levels were not statistically significant (P = 0.063). Levels of PGC-1α and LDH B were higher in the CT group than in the IT group. Conclusion: We concluded that CT has a greater effect on energy metabolism in the heart than IT. © 2020 Journal of Natural Science, Biology and Medicine Published by Wolters Kluwer - Medknow.