AIMS: Prone positioning is increasingly used for treating coronavirus disease 2019 (COVID-19)-induced acute respiratory distress syndrome (ARDS). In these high-risk patients for cardiovascular events who may spend more than 16 h a day in the prone position, an adequate monitoring of electrocardiogram (ECG) is mandatory. However, effects of prone positioning on the ECG are unknown as is the validity of the ECG recorded with electrodes placed dorsally. We aimed to compare ECG data obtained in the prone position from five electrodes positioned conventionally and dorsally, and to assess the effects of the change of position (from supine to prone) on the ECGs in patients with COVID-19 ARDS. METHODS AND RESULTS: In patients with COVID-19 ARDS for whom the prone position was indicated, seven-lead ECG (frontal plane leads and V6) performed in the supine and the prone position with electrodes positioned conventionally and dorsally were compared. A total of 22 patients [20 (91%) males] were included. Among them, 10 (45%) patients had structural or ischaemic heart disease. After prone positioning, PR duration significantly increased and QRS duration significantly decreased whereas QT interval did not significantly change. In the prone position, there were excellent correlations between QRS axis, PR, RR, QRS, and QT intervals durations measured with electrodes placed on the torso and dorsally (with no change in the position of V6). CONCLUSION: Prone positioning induced significant change in the ECG. In the prone position, ECG can be reliably monitored with four electrodes translated from conventional position to the back and with a precordial electrode left in V6 position.