The learning curve for the novel RHYTHMIA HDx™ 3-dimensional electroanatomic system is unknown. Retrospective data collection was carried out at 3 U.K. centers from the introduction of RHYTHMIA HDx™ (Boston Scientific, Marlborough, MA, USA) and associated mapping and ablation catheters. Patients were matched with controls using the CARTO®3 mapping system (Biosense Webster Inc., Diamond Bar, CA, USA). Fluoroscopy, radiofrequency ablation, and procedure times; acute and long-term success; and complications were assessed. A total of 253 study patients along with 253 controls were included. Significant correlations existed between procedural efficiency metrics and center experience for de novo atrial fibrillation (AF) ablation (procedure time, Spearman’s ρ = −0.624; ablation time, ρ = −0.795; bothP< .0005) and de novo atrial flutter (AFL) ablation (ablation time, ρ = −0.566; fluoroscopy time, ρ = −0.520; bothP= .001). No correlations existed for other assessed atrial arrhythmias. For de novo AF and AFL, metrics significantly improved after 10 procedures in each center (procedure time [AF only,P= .001], ablation time [AF,P< .0005; AFL,P< .0005], and fluoroscopy time [AFL only,P= .0022]) and became comparable to those of controls. Acute success and long-term success did not experience significant improvements with experience, but they were comparable to the control group throughout. Complications with RHYTHMIA HDx™ were comparable to those associated with CARTO®3. In conclusion, a short learning curve exists with the use of RHYTHMIA HDx™ for standardized procedures (de novo AF/AFL). Procedural performance improved and became comparable to that seen with CARTO®3 following 10 cases at each center. Clinical outcomes at 6 and 12 months and complications were no different from those observed in controls.