A 10-year-old boy presented with complaints of poor weight gain, progressively increasing dyspnea since early childhood, and orthopnea. Echocardiogram was suggestive of cor triatriatum. Cor triatriatum is a rare congenital cardiac anomaly in which the left atrium (cor triatriatum sinister) or the right atrium (cor triatriatum dextrum) is divided into two compartments by an abnormal fibromuscular septum usually with an opening between the two chambers associated with varying degrees of obstruction of the pulmonary veins. The pulmonary venous return is followed by pulmonary arterial hypertension. Cor triatriatum literally means a heart with three atria (triatrial heart), namely, the superior chamber, the inferior chamber or the true atrium, and the atrial appendage. This anomaly occurs in 0.4% of patients with congenital heart defects, with a slight male predominance. The present case of cor triatriatum sinister is being reported in view of the fact that the child remained undiagnosed till the age of 10 years, despite being “sick since a little boy” requiring multiple hospital admissions for chest infections. He had been receiving treatment for “chest problem” and had been on bronchodilators. The classical echocardiographic findings would be of academic interest as well.