Double Sequential External Defibrillation (DSED) represents an alternative treatment of refractory ventricular fibrillation (rVF) in out-of-hospital cardiac arrest (OHCA). The procedure consists of two defibrillators that administer shocks at the same time. Currently, the procedure is not initiated before at least three failed attempts with one defibrillator. This can delay the potential benefits of establishing DSED earlier in the treatment. Studies have shown that early defibrillation is crucial for survival in OHCA patients, and in 2022, a clinical trial showed that survival in patients treated with DSED was higher compared to standard treatment. The effect of initiating OHCA treatment is unknown. The DUALDEFIB trial seeks to investigate if treating OHCA patients with DSED as an initial treatment will increase survival and provide improved neurological outcome.