Localization of digoxin in sheep myocardium by immunofluorescent microscopy

6 newborn and 6 adult sheep were treated intravenously with digoxin for 2 weeks prior to sacrifice. Plasma and myocardial concentrations of digoxin were determined at steady state; the myocardial/plasma digoxin ratio was similar for the newborn and adult sheep. An immunofluorescent technique was used to localize digoxin within the myocardium. The pattern of fluorescence also did not vary with age. These studies show no age-related differences in the penetration or localization of digoxin within the heart. A simple immunofluorescent technique for the localization of digoxin within the heart is described.