Hi! Chest congestion can be due to respiratory as well as cardiological causes. Respiratory causes include lung injury due to drugs, chemicals, infections etc. But cardiological causes are far more common. Basically when the left side of your heart malfunctions in some way it is unable to pump blood to your body. As a result a back pressure is created due to stasis of blood in the left side of your heart. It is finally transmitted to your lungs. The increased pressure in your lungs causes the blood vessels in your lungs to leak out fluid which results in chest congestion. Your doctor must have suspected some cause like mitral stenosis or regurgitation or coronary artery disease or cardiomyopathy or some such condition. So he referred you to a cardiologist. It might not have been obvious simply from vital signs. A thorough clinical examination and investigations like electrocardiogram and echocardiogram will help detect the actual cause. Hope this helps.