Although a high-resolution three-dimensional mapping system has made it possible to treat complicated atrial tachyarrhythmia (AT), there remain cases that are difficult to diagnose and treat. ^1,2 When a single atrial tachycardia is present and stable, mapping is relatively easy. However, when multiple different ATs alternately appear, mapping and diagnosis of those are more difficult. Parallel mapping module is well known as a good option to simultaneously map two or more different ATs when they alternately appear. ³ When performing parallel mapping of two different ATs, one bipolar signal of the reference catheter is used as a timing reference and a cycle length filter is used for differentiating AT1, AT2, and others, including sinus rhythm, fusion beats, or catheter-induced premature atrial complex. Therefore, it has some limitations for differentiating multifocal ATs. We present a case wherein multifocal ATs were successfully eliminated by combining parallel mapping module and dual-chamber intra-cardiac pattern matching technique that we have previously reported. ⁴