Although radiofrequency catheter ablation (RFCA) is indicated in electrical storm (ES) refractory to antiarrhythmic drugs, its most appropriate timing has not been determined. Our objective is to analyse the impact of the timing of RFCA on 30-day mortality in patients with ES and previous scar-related systolic dysfunction. In this multicenter study we analysed 104 patients (age: 72±10, LVEF: 30±6%) attended consecutively due to an ES caused by monomorphic VT. Sixty-four subjects were treated with RFCA (mean time from admission=83±67 hours) and 40 were not. Upon admission 25 (24%) individuals had severe heart failure. Mortality rate at 30 days was 24 (23%) patients. RFCA was associated with a reduction of 30-day mortality (HR=0.2; p=0.008). After showing a positive correlation between the time of the RFCA (hours) and survival at 30 days (C-statistic=0.77; p<0.001), we found that only subjects ablated >48h after admission had lower mortality at 30 days than those treated conservatively: 38% (no RFCA) vs. 30% (RFCA ≤48h) vs. 7% (RFCA >48h) (Adjusted HR for RFCA >48h vs. others=0.2; p=0.007). Among the patients ablated, those who were non-inducible had lower 30-day mortality: 8% vs. 29% (p=0.03). Extracorporeal membrane oxygenation (ECMO) was associated with a higher rate of non-inducibility in RFCA >48h (100% vs. 76%; p=0.03), but not in RFCA ≤48h (60% vs. 60%; p=1). In conclusion, among high risk patients with ES, RFCA performed >48 hours after admission is associated with a reduction in 30-day mortality. In such subjects, the probability of successful RFCA increases when performed under ECMO support.