The aim of this study was to analyse the effect of sulforaphane (SFN) in cultures of adult cardiomyocytes, evaluating oxidative stress at different times. Cells were isolated, cultured, and divided into 4 groups: Control, SFN (5μM), H₂O₂ (5μM), and SFN+H₂O₂ (5μM both), and subdivided into groups undergoing 1 or 24 h of SFN incubation. After 1 h of incubation, reactive oxygen species production was 40% lower in the SFN group than the Control, and lipid peroxidation was 63% higher in the H₂O₂ group than the Control, and it was reduced in both of the SFN groups. The SOD activity was 59% higher in groups incubated for 24 h than in those incubated for 1 h. Protein expression of SOD-1 and SOD-2 was higher in the 24-h groups compared to the 1-h groups (55% and 24%, respectively). The Nrf2 protein expression in the 1-h groups was 17% higher than in the 24-h groups, and the SFN + H₂O₂ group had 40% more Nrf2 than the Control in the 1-h groups. Unlike Nrf2, the PGC-1α expression was 69% higher in the 24-h groups in relation to the 1-h groups. Regarding the 24-h groups, the SFN and SFN+H₂O₂ groups were higher than the Control (32% and 33%, respectively), and the SFN+H₂O₂ group was increased (21%) compared to H₂O₂. SFN had a protective action against oxidative damage, but had no effect on the antioxidant enzymes analyzed. The different responses in the expression of Nrf2 and PGC-1α in relation to the incubation times, draws attention to the importance of establishing a timeline of the action of SFN, since there appears to be a temporal difference in its mechanism in adult cardiomyocytes.