CYP2C9 and heart failure: First dose monitoring for patients with sinus bradycardia, first- or second-degree atrio-ventricular block or a history of myocardial infarction or heart failure. Baseline: CYP2C9 genotyping; vital signs and ECG; full blood count; serology (VZV, HIV 1 and 2); ocular examination; LFTs. Follow-up: full blood count; ocular examination at 3 months; skin examination; LFTs; neurologic and psychiatric examination