 Patients randomized to use of the Cardionet device will have a home patient educator install the device within 24 hours after enrollment. Electrocardiographic summaries will be reviewed by a research physician three times a week and treatment decisions will be made based on a summary of 24-hour rate control. The physician will contact the patient by telephone and make medication adjustments per protocol. Three-times-weekly transmissions and medication adjustments will continue until adequate rate control is achieved over a period of 24 hours. 