Using intra-cardiac echocardiography in anaesthetised swine we tested the hypotheses that embolised air (i) passes immediately through the right atrium into the ventricle; (ii) persists in the right ventricle for a long time; (iii) is detectable for longer within the right ventricle or main pulmonary artery than the right atrium, and (iv) right ventricular aspiration recovers more air than right atrial aspiration. Following intravenous injection of different air volumes the air appeared in the right atrium in a mean (95% CI) of 3 s (2.5-3.5 s) and almost simultaneously in the right ventricle after 5 s (3.9-6.0 s), but air persisted for longer in the right ventricle (420 s; (367-473 s)) and pulmonary artery (541 s; (475-606 s)) than in the right atrium (404 s (353-457 s)), particularly with larger air volumes and in the semi-upright position. More air was recovered via a right ventricular catheter than an atrial catheter (52% vs 25%, p < 0.01).