The success of prophylactic digitalization in reducing the incidence of supraventricular tachyarrhythmias (SVT) was studied in 140 randomly grouped, consecutive patients undergoing myocardial revascularization operations. The test group received either 1 or 1.5 mg. of digoxin the day before operation and were maintained postoperatively on 0.25 mg. of digoxin daily. There was a significant increase (p less than 0.05) in the incidence of SVT in the treated patients (17 of 61 or 27.8 percent) vs. the untreated patients (nine of 79 or 11.4 percent). There was no significant difference in SVT with the two digitalization dosage levels (31.6 percent with 1 mg. vs. 21.7 percent with 1.5 mg.). Prophylactic digitalization demonstrates no benefit in the prevention of SVT following myocardial revascularization and may, in fact, predispose the patient to these arrhythmias.