Target site for adenosine in arrhythmia treatment.

• A. Blood Vessels
• B. Nerve Tissue
• C. Cardiac Tissue
• D. Skeletal Muscle

Answer: (C)

The key idea is that adenosine stops certain fast heart rhythms by momentarily blocking conduction in the heart’s electrical pathway, specifically the AV node. It binds to A1 receptors in cardiac tissue, which opens potassium channels and lowers cAMP, causing hyperpolarization and a rapid decrease in calcium currents. This slows and briefly halts conduction through the AV node and increases its refractory period, effectively interrupting the re-entrant circuit that sustains the tachycardia and allowing normal rhythm to resume. While adenosine can affect other tissues, the therapeutic effect for arrhythmia control comes from its action on cardiac tissue, especially the AV node. The other tissues listed are not the site where this acute antiarrhythmic effect is achieved.