The case of a neonate with isolated pulmonary valvular insufficiency resulting in heart failure and death is reported. Only two previous examples of symptomatic pure pulmonic insufficiency have been described: one similar case with intrauterine hydrops and death, 30 minutes after birth, and one adolescent with marked cardiac enlargement. Although this anomaly is usually considered to be a benign cardiac lesion, available experimental data and analysis of patients with additional lesions indicate that deleterious effects of pulmonary insufficiency may be anticipated if there is 1) little valve tissue and thus gross pulmonary regurgitation, 2) pulmonary hypertension, and/or 3) increased blood flow across the abnormal pulmonary valve.