Selective inhibition of funny sodium channels (I_f), prolonging slow depolarization phase 4.↓ SA node firing; negative chronotropic effect without inotropy. Reduces cardiac O₂ requirement.

Clinical use: - Chronic stable angina in patients who cannot take β-blockers. - Chronic HF with reduced ejection fraction.

Side effect: Luminous phenomena/visual brightness, hypertension, bradycardia.