A method and device for providing ventilation gas to a patient during cardiopulmonary resuscitation. The device comprises: a gas source for supplying oxygen to the bronchi of the patient and a switch valve for initiating and terminating the gas supply. The switch valve is operated synchronous with the cardiopulmonary resuscitation cycle so that the switch valve operates with the same cycle as the cardiopulmonary resuscitation cycle but off-set in relation to the cardiopulmonary resuscitation cycle. The gas supply is initiated between 25% and 2% of the cycle time before the start of a compression stroke and is terminated between 2% and 30% of the cycle time after the start of a compression stroke. Alternatively, the gas supply is initiated between 25% and 48% of the cycle time after the termination of a compression stroke and is and terminated between 52% and 80% after the termination of a compression stroke.