Hyperpolarized 129Xe MRI is a powerful probe of lung ventilation, perfusion and gas-exchange. It can be used in both clinical and preclinical settings, where the latter enables rapid discovery of new applications and early testing of therapies in animal models. However, preclinical hyperpolarized gas MRI has been limited to a few expert sites, owing to the challenge of reliably delivering hyperpolarized gas to small animals. Here, we present a constant-volume ventilator that allows for high-resolution hyperpolarized gas imaging and spectroscopy during precisely controlled multi-breath acquisitions. The ventilator is compact, portable, and easy to duplicate and disseminate.