A 4-month old, male castrated, Domestic Longhair kitten was presented to the Emergency Service in November 2008 for respiratory distress. Upon presentation, he was hypothermic, cyanotic, dyspneic, and coughing. Dull lungs sounds were ausculted bilaterally and a Grade III-IV/VI holosystolic murmur was ausculted at the left heart base. A diagnosis of left sided congestive heart failure secondary to a cardiac malformation was made following thoracic radiographs. Echocardiography disclosed severe bi-atrial dilation, an atrial septal defect, abnormal conformation of the mitral and tricuspid valves, and communication between all four heart chambers. Based on these findings, a diagnosis of incomplete endocardial cushion defect was made. Due to the grave prognosis associated with this condition and the severity of clinical signs, the kitten was euthanized. A necropsy followed and revealed a complete endocardial cushion defect.