Background: Doppler microembolic signals (MES) occur during atrial fibrillation ablation despite of permanent flushed transseptal sheaths, frequent controls of periprocedural coagulation status and the use of irrigated ablation catheters Purpose: To investigate the number and type of MES depending on the procedure time, prespecified procedure steps, the activated clotting time (ACT) during the ablation procedure and the catheter contact force. Methods: In a prospective trial, 53 consecutive atrial fibrillation patients underwent pulmonary vein isolation by super-irrigated “point-by-point” ablation. All patients underwent a periinterventional, continuous transcranial Doppler examination (TCD) of the bilateral middle cerebral arteries during the complete ablation procedure. Results: An average of 686±226 microembolic signals were detected by permanent transcranial Doppler. Thereby, 569±208 signals were differentiated as gaseous and 117±31 as solid MES. The number of MES with regard to defined procedure steps were as follows: gaseous: [transseptal puncture, 26 ± 28; sheath flushing, 24±12; catheter change, 21±11; angiography, 101±28; mapping, 9±9; ablation, 439±192; protamine administration, 0±0]; solid: [transseptal puncture, 8±8; sheath flushing, 9±5; catheter replacement, 6±6; angiography, not measurable; mapping, 2±5; ablation, 41±22; protamine administration, 0±0]. Significantly less MES occurred with shorter procedure time, higher ACT and the use of tissue contact force monitoring. Conclusion: The current study demonstrates that during atrial fibrillation ablation using irrigated, “point-by-point” RF ablation, masses of microembolic signals are detected in transcranial ultrasound especially in the period of RF current application. The number of MES depends on the total procedure time and the reached ACT during ablation. The use of contact force monitoring might reduce MES during RF ablation.