The occurrence of severe sinus node dysfunction in 10 patients (three males and seven females; mean age 78.5 +/- 3.4, range 57-92 years) receiving oral diltiazem therapy (mean 190 +/- 20 mg/24 h, range 90-300) is described. Six of them were concomitantly taking amiodarone and/or beta-blocking agents. On admission, seven patients exhibited systemic hypotension and nine complained of asthenia and/or dizziness or drowsiness. ECG findings showed in all a persistent sinus arrest with atrial, junctional or ventricular escape, leading to a mean heart rate of 40.2 +/- 3 beats.min-1 (range 25-56). All patients had chronic renal failure on biological tests, with a mean endogenous creatinine clearance of 25 +/- 3 ml.min-1 (range 12-36). Intravenous calcium hydrochloride (mean 1.4 +/- 0.2 g, range 1-2), given in nine patients, rapidly restored stable sinus activity in seven. We suggest that diltiazem should be given cautiously to ageing patients with chronic renal failure, and confirm the efficacy of intravenous calcium in reversing calcium channel blocker toxicity on sinus node.