We investigated the effects of outdoor pressure fluctuations on natural ventilation in a room with two openings. One opening is exposed to an oscillating outdoor pressure and the other is exposed to a fixed neutral pressure. The ventilation airflow rate depends on the amplitude and period of the outdoor pressure fluctuations, the room volume, and the sizes of the openings. Dimensionless parameters are derived from the governing equations that determine indoor pressure responses due to outdoor pressure fluctuations. The pressure responses and the airflow rates through the openings are obtained using a fourth-order Runge-Kutta method. The flow regions are categorize into a synchronized region, an opening resistance region, and a transition region, depending on the dimensionless parameters. Applications are considered using an example building space to investigate the effective air change rates depending on the size of the openings and the period of wind pressure fluctuations.