The failure of the hole between the two atria to close after birth leads to a disorder called ASD primum. The most common problems with an opening found in the heart with Lutembachers syndrome is Ostium Secundum. Ostium Secundum is a hole that is found within the flap of tissue (septum primum) that will eventually close the hole between the two atria after birth. With either type of ASD, ASD will usually cause the blood flow from the right atrium to skip going to the right ventricle and instead flow to the left atrium. If mitral stenosis (the hardening of flap of tissue known as a valve which opens and closes between the left atrium and ventricle to control blood flow) is also present, blood will flow into the right atrium through the hole between the atria wall instead of flowing into the left ventricle and systemic circulation. Eventually this leads to other problems such as the right ventricle failing and a reduced blood flow to the left ventricle.In addition to the ASD, MS can either be acquired (present either from an episode of rheumatic fever or the mother has or had rheumatic fever during the pregnancy) or congenital (the child being born with the disorder). With the combination of both ASD and MS, the heart can be under severe strain as it tries to move blood throughout the heart and lungs.
Then blood pass to right ventricle this will increase pulmonary artery pressure  Due to the incorrect blood flow, symptoms such as fatigue (from decreased systemic blood flow), palpitations (from blood flowing from left atria to right atria), weight gain, edema, right upper chest pain (all caused from the left to right atria blood flow), and paroxysmal nocturnal dyspnea (shortness of breath during sleep), orthopnea (difficulty in breathing while lying down), and hemoptysis or coughing up blood (all caused by small ASD that cause blood flow from left to right atria). Atrial Septal Defect Ostium secundum
During the more common form of Lutembachers syndrome, ASD Ostium secundum, a hole will form in the flap of tissue (septum primum) that should close between the two atria after birth. With the onset of a hole created in the tissue flap that closes the larger hole between the left and right atrium, blood can again flow from the left atrium to the right. Ostium secundum causes many of the same symptoms seen in ASD primum. With either type of ASD, blood will flow from the right atrium skipping the right ventricle (or very little flowing into the ventricle) and instead flow to the left atrium introducing the possibility of blood lacking oxygen to go the rest of the body. Sometimes, the direction of blood flow is largely determined by the left and right ventricle ability to squeeze (contract) and relax (compliance).Apart from congential or birth defects causing ASD, ASD is thought to be also acquired.