Induction of ventricular arrhythmias in mice with chronic pressure overload. (A) Representative traces showing polymorphic ventricular tachycardia (VT) induced by programmed ventricular stimulation in a mouse subjected to transverse aortic constriction (TAC). RV, right ventricle; RA, right atrium. Ten pacing stimuli (S1; a coupling interval is 80–90 ms) followed by 2–3 extra stimulations (S2-4) were used to induce VT. (B) Effects of chronic pressure overload on left ventricular ion channel gene transcription 4 weeks after TAC or sham operation. Graphs show relative expression levels of SCN5A, CACNA1c, KCND2, Kchip2, KCNJ2, KCNH2 and KCNJ11 mRNA normalized to corresponding GAPDH mRNA levels. The mean relative level of each mRNA in sham-operated WT mice was assigned a value of 1.0. Values are means ± SEM (n = 8 each). *P < 0.01 versus sham-operated mice in each genotype.