Cor triatriatum sinister (CTS) is an extremely rare congenital cardiac malformation characterized by the presence of a fibromuscular membrane subdividing the left atrium into two chambers. Although respiratory symptoms are often observed in patients with this anomaly, wheezing is an unusual clinical presentation. We report on a child, born and resident in the Brazilian Amazonia, with a history of recurrent episodes of 'asthma' who was subsequently found to have CTS. After successful surgical correction of the cardiac congenital malformation, the child became symptom free. This case highlights the importance of investigating by cardiologic assessment children with worsening wheezing that do not respond well to appropriate medical management.