An accessory device for a twelve-lead electrocardiography (ECG) apparatus includes a blanket. The ECG apparatus includes an ECG machine that has ten first electrical couplers, and ten electrodes each having a second electrical coupler. The blanket includes a sheet body configured to cover the body of a patient and formed with ten holes that are arranged according to a standard electrode placement for twelve-lead ECG measurement and that are configured to permit the second electrical couplers of the ten electrodes to extend therethrough, respectively.
