We report a case of a 56-year-old man diagnosed with non-ischemic cardiomyopathy in 2017 with progressive decline in left ventricular systolic function and frequent hospitalisations for heart failure in the context of a presumed atrial fibrillation with high ventricular rate. Electrocardiographic changes after adenosine administration raised the suspicion of dual atrioventricular nodal non-reentrant tachycardia, a diagnosis that was confirmed by electrophysiological study, making adenosine a potential diagnostic aid in such cases. The ablation of the slow pathway terminated the tachycardia and led to a marked improvement in symptomatology and echocardiographic parameters.