A woman in her sixties presented with a history of progressive shortness of breath, palpitations, and feeling of chest heaviness for the last eight months. To rule out underlying obstructive coronary artery disease, an invasive cardiac catheterization was planned. To assess the hemodynamic significance of the lesion, resting full cycle ratio (RFR) and fractional flow reserve (FFR) values were measured. During this procedure, almost immediately after starting IV adenosine infusion, the patient went into atrial fibrillation which was reversed by IV aminophylline. Awareness of this uncommon effect of adenosine on the cardiac electrical pathways merits knowledge and a thorough follow-up testing of these patients is justified.