A, phenylephrine-induced bradycardia, expressed as change in interpulse interval (ms) per change in mean arterial blood pressure (mmHg), in response to pressor challenge was increased in anaesthetized nNOS+/−, +EX mice treated with Ad.nNOS compared to treatment with Ad.eGFP adenovirus (*P < 0.05, unpaired t test). Ad.nNOS treatment failed to have a significant effect on phenylephrine-induced bradycardia in WT, +EX mice, although Ad.nNOS increased bradycardia in WT, −EX mice by 64% compared to Ad.eGFP (P < 0.05, unpaired t test; data not shown). B, bradycardia to vagal nerve stimulation (5 Hz) in isolated atria in vitro was enhanced in nNOS+/−, +EX mice treated with Ad.nNOS compared to treatment with Ad.eGFP adenovirus (*P < 0.01, unpaired t test).