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Figure 1 Left panels. Effects of d,l-sotalol on (A) heart rate (HR), (B) PR interval duration (PR) and (C) QT interval duration (QT) in unaffected dogs (n = 9, solid circle) and affected dogs (n = 6, solid triangle). See protocol in Methods section. (B) ^#p < 0.05, that is, the two curves are parallel and significantly separated (two-way analysis of variance). (C) For better clarity, we plotted the sotalol-induced increase in QT interval. Values of the QT interval at t = 0 were 227 ± 5 ms in unaffected dogs and 219 ± 8 ms in affected dogs (NS vs. unaffected). *p < 0.05, that is, the effect of sotalol is greater in affected dogs (two-way analysis of variance performed on raw QT values). Right panels. Typical electrocardiogram recordings obtained in (D) in unaffected dog and (E) an affected dog under controlled conditions (top) and 15 min after the second injection of d,l-sotalol (bottom). Vertical bars, 20 mV; horizontal bars, 1 s. See text for further explanation. bpm = beats per min.