Can pectus excavatum press on the heart or lungs and become fatal?

Doubtful: I couldn't locate a controlled study on long-term effects if surgery is not done. In most cases the condition is cosmetic, and there were no reported deaths. Severe pectus excavatum does decrease lung and cardiac function, however, basically through compression and smaller volumes. A pediatric surgeon would be able to give you a better idea of the future after checking the individual patient.

No: Pectus excacatum can press on structures within the chest. These structures, ie heart and lungs do move in response to the pressure of the sternum. This can effect the efficiency and result in chest pain, shortness of breath and decreased exercise tolerance. A nuss procedure is a minimally invasive technique that can correct this defect.