Ivabradine lowers the heart rate by inhibiting the cardiac pacemaker current that is responsible for diastolic depolarization. Ivabradine acts on the sinus node as follows: With a sufficient depolarization of the membrane, conversion of ATP into cAMP results in opening of the If-channel, creating a slow inward current of Na+. After opening, the systolic polarization phase is followed by the diastolic depolarization phase. Ivabradine inhibits the flow through
the If-channel, thereby prolonging the depolarization phase. The heart frequency will then decrease, as will the oxygen demand of the heart. The most important side effect is the appearance of light flashes (phosphenes). The agent can be used in patients with angina pectoris when ß-blockers are insufficiently effective or not tolerated by the patient, provided that the heart rate is at least 60 bpm at the beginning of treatment.