Right atrioventricular valve insufficiency and bilateral congestive heart failure were identified in a carpet python (More -lia spilota variegata ) with the aid of colour Doppler echocardiography, electrocardiography and radiography . The snake failed to respond to diuretic therapy and was euthanased. Based on this case, it appears that bilateral congestive fail-ure is feasible in univentricular animals with lesions restricted to one side of the heart. Loop diuretic therapy may be inappropriate in non-crocodilian reptiles because reptiles lack a loop of Henle.