Direct current cardioversion (DCCV) is a widespread method to restore sinus rhythm in patients with atrial fibrillation. It is a safe and effective method of treating atrial fibrillation. In this study, the investigators want to compare two algorithms. The rational one, with lower initial energy and the second one with the maximum possible shock energy.

Inclusion Criteria:

1. Patients must have atrial fibrillation or atrial tachycardia.
2. Patients must be on therapeutic anticoagulation at least three weeks prior to DCCV or undergo esophageal echocardiography to rule out intracardiac thrombus.
3. Patients come on an empty stomach.
4. Patients must be over 18 years of age.
5. Patients must provide verbal and written informed consent to participate in the study.

Exclusion Criteria:

1. Omitting oral anticoagulant treatment in the last three weeks.
2. Unclear time of onset of palpitations in acute patients without anticoagulation therapy.
3. A different type of arrhythmia than atrial fibrillation or atrial tachycardia.