Only one SAN–RA preparation from the MCT-induced PAH group showed premature atrial beats with retrograde conduction from the RA to the SAN (Figure 4B), and ET-1 could induce more premature beats or short runs of atrial tachycardia (1 of 9 vs. 7 of 9, p < 0.05) in SAN–RA preparations from the MCT-induced PAH group. The gene discussed is EDN1; the disease is atrial tachycardia.