Purpose: The purpose of this study was to identify which group of cardiac patients is most at risk when dental extractions are performed under local anesthesia. Patients and Methods: Forty cardiac patients who had dental extraction under local anesthesia (Mepivacain HCl three percent) were connected to a Holter monitor for 24 hours starting 1 hour before the procedure. Of the 40 patients, 24 had coronary artery disease, 12 had valvular disease, 3 were being treated with antiarrhythmic drugs, and 1 had malignant arterial hypertension. Sixteen patients were being treated with digoxin. The electrocardiogram was analyzed for the number of premature beats, ST depression, and cardiac rhythm. A mean rate was calculated for the first 2 hours after injecting the local anesthetic and surgical procedure, and for the subsequent 22 hours. Results: All electrocardiographic changes occurred during the first 2 hours after injecting the local anesthetic. When the mean rate of that period was compared with the remaining 22 hours, new pathologic signs of arrhythmia, tachycardia, or ST depression were seen in 14 patients (35%). Of these, 12 were being treated with digoxin. Conclusion: Patients being treated with digoxin for atrial fibrillation or congestive heart failure are more prone to complications during dental extractions under local anesthesia than other cardiac patients.