A manual ventilation or resuscitation device is provided. The body of the device has rigid panels that encompass a sealed volume and are movable with respect to each other. The body has a displacement in a direction of a hand displacement and at least one other direction. A size adjuster adjusts the body displacement(s) between the states. A frequency adjuster adjusts the time to restore the volume or to adjust the time to compress the volume. The body provides an ergonomic fit to a user's hand, which reduces fatigue. The volume and/or frequency adjustments provide a user with reliance on a more or less constant tidal volume and tidal rate. Such adjustments allow usage of the device on any patient, regardless of individual factors such as physical condition, body/lung size, age and sex. Multiple devices could easily be stacked or nested with each other, which reduces storage space.