Myocardial amiodarone and desethylamiodarone concentrations in patients undergoing cardiac transplantation. Myocardial amiodarone and desethylamiodarone concentrations were measured at multiple sites in the explanted heart in four patients who underwent cardiac transplantation. Patients were taking amiodarone, 200 to 400 mg/day (mean 300 +/- 115), for 88 to 428 days (mean 229 +/- 148). The mean cumulative dose was 58 +/- 21.3 g. Plasma amiodarone concentration in three subjects was 204, 312 and 419 ng/ml and desethylamiodarone concentration was 268, 513 and 880 ng/ml, respectively. Significant interindividual variability in myocardial concentrations of amiodarone and desethylamiodarone was observed (p less than 0.05). Mean myocardial amiodarone concentration ranged from 4 +/- 1.0 to 29 +/- 17.2 micrograms/g (p less than 0.05); mean desethylamiodarone concentration ranged from 22 +/- 8.8 to 141 +/- 102.5 micrograms/g (p less than 0.05). At each site, save for fat, myocardial desethylamiodarone concentration was higher than amiodarone concentration. Greater intraindividual variability was observed in myocardial desethylamiodarone compared with amiodarone concentration particularly in septal and scar tissue (p = NS). No significant relation was found between myocardial concentration and duration of treatment. In patients with significant ventricular disease, usefulness of plasma amiodarone and desethylamiodarone concentration to estimate myocardial concentration is limited by intra- and interindividual variability. 