We present a retrospective review of twelve cases of Irukandji syndrome associated with pulmonary oedema. This is a life-threatening envenoming due to a presumed jellyfish sting throughout Northern Australia, although only one case occurred outside North Queensland. Patients presented with significant and ongoing pain, tachycardia and hypertension. Half the patients became hypotensive requiring inotropic support. Cardiac echocardiography revealed significant cardiac dysfunction. Six patients required ventilatory support. There was no death reported due to pulmonary oedema, but one patient died of intracerebral haemorrhage. We believe patients may develop a toxin associated cardiomyopathy, and jellyfish other than Carukia barnesi may be responsible. As there is confusion with nomenclature, Carukia barnesi should be known as the Barnes jellyfish, and the diagnosis of cardiotoxic marine envenoming is suggested for any patient who has been stung by a jellyfish, develops no or minimal skin markings, and develops cardiogenic pulmonary oedema associated with Irukandji syndrome.