A 19 year old Standardbred gelding and a 5 year old Quarter Horse mare experienced an episode of air embolism due to a dislodged catheter cap. Initial clinical signs in the gelding included tachycardia, arrhythmia, tachypnoea and disorientation. The mare showed agitation, selfmutilation due to severe pruritus, tachycardia with a mill-wheel murmur and tachypnoea. Echocardiography revealed air bubbles in the right and left side of the heart, the pulmonary vessels and the aorta. An anatomical abnormality was excluded by a bubble study, proving a paradoxical air embolism. Both horses received symptomatic treatment and recovered. Air embolism rarely occurs in horses. The extent of air embolism can be shown with echocardiography, which seems to allow a better evaluation of the condition and might be helpful in determining which clinical signs are to be expected.