Some recent research has suggested that a proportion of cases of migraine may be caused by PFO. While the exact mechanism remains unclear, closure of a PFO can reduce symptoms in certain cases. This remains controversial; 20% of the general population has a PFO, which for the most part, is asymptomatic. About 20% of the female population has migraines, and the placebo effect in migraine typically averages around 40%. The high frequency of these facts finding statistically significant relationships between PFO and migraine difficult (i.e., the relationship may just be chance or coincidence). In a large randomized controlled trial, the higher prevalence of PFO in migraine patients was confirmed, but migraine headache cessation was not more prevalent in the group of migraine patients who underwent closure of their PFOs.

A patent foramen ovale (PFO) is a small channel that has some hemodynamic consequence; it is a remnant of the fetal foramen ovale, which normally closes at birth. In medical use, the term "patent" means open or unobstructed. In about 25% of people, the foramen ovale fails to close properly, leaving them with a PFO or at least with what some physicians classify as a "pro-PFO", which is a PFO that is normally closed, but can open under increased blood pressure. On echocardiography, shunting of blood may not be noted except when the patient coughs.

Clinically, PFO is linked to stroke, sleep apnea, migraine with aura, and decompression sickness. No cause is established for a foramen ovale to remain open instead of closing naturally, but heredity and genetics may play a role.

The mechanism by which a PFO may play a role in stroke is called paradoxical embolism. In the case of PFO, a blood clot from the venous circulatory system is able to pass from the right atrium directly into the left atrium via the PFO, rather than being filtered by the lungs, and thereupon into systemic circulation toward the brain. PFO is common in patients with atrial septal aneurysms (ASA) which are also linked to cryptogenic (i.e. of unknown cause) strokes.

PFO is more prevalent in patients with cryptogenic stroke than in patients with a stroke of known cause. While PFO is present in only 25% in the general population, the probability of someone having a PFO increases to about 40 to 50% in patients who have had a cryptogenic stroke. Statistically speaking, this is particularly true for patients who have a stroke before the age of 55.

PFO is not treated in the absence of other symptoms, and no consensus exists on treatment of PFO even in the presence of transient ischemic attack or stroke. Moreover, no "gold standard" treatment option is known. However, treatments for PFO include surgical closure and percutaneous device closure, as well as medical therapies such as anticoagulant therapy, and antiplatelet agents.

Research studies of the efficacy of surgical closure treatments versus medical therapies of PFOs in preventing the recurrence of strokes have been conducted; the results are mixed, although “as-treated” and “per-protocol” analyses were positive for closure devices.

PFO closure devices may be implanted via catheter-based procedures, and using a variety of closure devices.

Debate exists within the neurology and cardiology communities about the role of a PFO in cryptogenic neurologic events such as strokes and transient ischemia attacks without any other potential cause. Some data suggest that PFOs may be involved in the pathogenesis of some migraine headaches. Several clinical trials are currently underway to investigate the role of PFO in these clinical situations.

In a retrospective analysis of over 1,300 newborns (born between 1996 and 2006) from 24 children’s hospitals in the United States, researchers at Cincinnati Children’s Hospital in Ohio found that babies with HLHS were more likely to be born in summer months, suggesting that seasonality and environmental factors may play a significant role in causation.

Presence of a cystic hygroma increases the risk of HLHS in a fetus.

Almost all cases of mitral stenosis are due to disease in the heart secondary to rheumatic fever and the consequent rheumatic heart disease. Uncommon causes of mitral stenosis are calcification of the mitral valve leaflets, and as a form of congenital heart disease. However, there are primary causes of mitral stenosis that emanate from a cleft mitral valve. It is the most common valvular heart disease in pregnancy.

Other causes include infective endocarditis where the vegetations may favor increase risk of stenosis. Other rare causes include mitral annular calcification, endomyocardial fibroelastosis, malignant carcinoid syndrome, systemic lupus erythematosus, whipple disease, fabry disease, and rheumatoid arthritis. hurler' disease, hunter's disease, amyloidosis.

The natural history of mitral stenosis secondary to rheumatic fever (the most common cause) is an asymptomatic latent phase following the initial episode of rheumatic fever. This latent period lasts an average of 16.3 ± 5.2 years. Once symptoms of mitral stenosis begin to develop, progression to severe disability takes 9.2 ± 4.3 years.

In individuals having been offered mitral valve surgery but refused, "survival" with medical therapy alone was 44 ± 6% at 5 years, and 32 ± 8% at 10 years after they were offered correction.

Preexisting diabetes mellitus of a pregnant mother is a risk factor that has been described for the fetus having TGV.

Hypoplastic right heart syndrome is less common than hypoplastic left heart syndrome which occurs in 4 out of every 10,000 births. [3].

This rare anomaly requires prenatal diagnosis since it needs immediate and emergency treatment. Pregnant women whose pregnancy is complicated with this anomaly should be referred to a level 3 hospital with pediatric cardiology and pediatric cardiothoracic surgical team.[3]

It can be associated with aortic stenosis.

Although its cause is poorly understood, situs ambiguous has been linked to family history of malformations and maternal cocaine use, suggesting both genetic and environmental factors play a role. Several genes in the TGF-beta pathway, which controls left-right patterning of viseral organs across the body axis, have been indicated in sporadic and familial cases of atrial isomerism.

There does not appear to be a screening method for prevention of heterotaxy syndrome. However, genetic testing in family members that display atrial isomerism or other cardiac malformations may help to discern risk for additional family members, especially in X-linked causes of heterotaxy syndrome.

A sinus venosus atrial septal defect is a type of atrial septal defect primarily associated with the sinus venosus.

They represent 5% of atrial septal defects.

They can occur near the superior vena cava or inferior vena cava, but the former are more common.

They can be associated with anomalous pulmonary venous connection.

For newborns with transposition, prostaglandins can be given to keep the ductus arteriosus open which allows mixing of the otherwise isolated pulmonary and systemic circuits. Thus oxygenated blood that recirculates back to the lungs can mix with blood that circulates throughout the body. The arterial switch operation is the definitive treatment for dextro- transposition. Rarely the arterial switch is not feasible due to particular coronary artery anatomy and an atrial switch operation is preferred.

Hypoplastic right heart syndrome is a congenital heart defect in which the right atrium and right ventricle are underdeveloped. This defect causes inadequate blood flow to the lungs and thus, a blue or cyanotic infant.[3]

Several genes have been identified in normal development of the right-left axis. These genes have been extensively researched. Gene mutations that lead to atrial isomerism is a growing area of research. Mutations in genes that encode proteins in the TGF-beta pathway, including NODAL, NKX2-5, and ZIC3, have been linked to tetralogy of fallot and hypoplastic left heart syndrome. Mutations in the ZIC3 gene, which encodes for the first zinc finger transcription factor, is linked to a 50% risk of atrial isomerism in families. It is also an X-linked disorder, so testing for ZIC3 mutations is highly encouraged in male births.

The most prevalent and best characterized genetic associations of heterotaxy include:

Cor triatriatum (or triatrial heart) is a congenital heart defect where the left atrium (cor triatriatum sinistrum) or right atrium (cor triatriatum dextrum) is subdivided by a thin membrane, resulting in three atrial chambers (hence the name).

Cor triatriatum represents 0.1% of all congenital cardiac malformations and may be associated with other cardiac defects in as many as 50% of cases. The membrane may be complete or may contain one or more fenestrations of varying size.

Cor triatrium sinistrum is more common. In this defect there is typically a proximal chamber that receives the pulmonic veins and a distal (true) chamber located more anteriorly where it empties into the mitral valve. The membrane that separates the atrium into two parts varies significantly in size and shape. It may appear similar to a diaphragm or be funnel-shaped, bandlike, entirely intact (imperforate) or contain one or more openings (fenestrations) ranging from small, restrictive-type to large and widely open.

In the pediatric population, this anomaly may be associated with major congenital cardiac lesions such as tetralogy of Fallot, double outlet right ventricle, coarctation of the aorta, partial anomalous pulmonary venous connection, persistent left superior vena cava with unroofed coronary sinus, ventricular septal defect, atrioventricular septal (endocardial cushion) defect, and common atrioventricular canal. Rarely, asplenia or polysplenia has been reported in these patients.

In the adult, cor triatriatum is frequently an isolated finding.

Cor triatriatum dextrum is extremely rare and results from the complete persistence of the right sinus valve of the embryonic heart. The membrane divides the right atrium into a proximal (upper) and a distal (lower) chamber. The upper chamber receives the venous blood from both vena cavae and the lower chamber is in contact with the tricuspid valve and the right atrial appendage.

The natural history of this defect depends on the size of the communicating orifice between the upper and lower atrial chambers. If the communicating orifice is small, the patient is critically ill and may succumb at a young age (usually during infancy) to congestive heart failure and pulmonary edema. If the connection is larger, patients may present in childhood or young adulthood with a clinical picture similar to that of mitral stenosis. Cor triatriatum may also be an incidental finding when it is nonobstructive.

The disorder can be treated surgically by removing the membrane dividing the atrium.

In PLSVC, the left brachiocephalic vein does not develop fully and the left upper limb and head & neck drain into the right atrium via the coronary sinus.

The variation, in isolation, is considered benign, but is very frequently associated with cardiac abnormalities (e.g. ventricular septal defect, atrioventricular septal defect) that have a significant mortality and morbidity. It is more frequent in patients with congenital heart defects.

Epidemiological data is elusive owing to the wide variety of clinical presentation. In the U.S., incidence is estimated to be at 5–10 cases per 100,000 per year. Minor compression of the inferior vena cava during pregnancy is a relatively common occurrence. It is seen most prevalently when women lie on their back or right side. 90% of women lying in the supine position during pregnancy experience inferior vena cava syndrome; however, not all of the women display symptoms.

In anatomy, a persistent left superior vena cava (PLSVC) is the most common variation of the thoracic venous system, is prevalent in 0.3% of the population, and an embryologic remnant that results from a failure to involute.

In the general population, obesity appears to be the most important risk factor for LAE. LAE has been found to be correlated to body size, independent of obesity, meaning that LAE is more common in people with a naturally large body size. Also, a study found that LAE can occur as a consequence of atrial fibrillation (AF), although another study found that AF by itself does not cause LAE. The latter study also showed that the persistent type of AF was associated with LAE, but the number of years that a subject had AF was not.

Obstructive sleep apnea (OSA) may be a cause of LAE in some cases. When an OSA event occurs, an attempt is made to breathe with an obstructed airway and the pressure inside the chest is suddenly lowered. The negative intrathoracic pressure may cause the left atrium to expand and stretch its walls during each OSA event. Over time, the repetitive stretching of the left atrium may result in a persistent left atrial enlargement.

Congenital stenosis of vena cava is a congenital anomaly in which the superior vena cava or inferior vena cava has an aberrant interruption or coarctation.

In some cases, it can be asymptomatic, and in other cases it can lead to fluid accumulation and cardiopulmonary collapse.

In TAPVC without obstruction, surgical redirection can be performed within the first month of life. The operation is performed under general anesthesia. The four pulmonary veins are reconnected to the left atrium, and any associated heart defects such as atrial septal defect, ventricular septal defect, patent foramen ovale, and/or patent ductus arteriosus are surgically closed. With obstruction, surgery should be undertaken emergently. PGE1 should be given because a patent ductus arteriosus allows oxygenated blood to go from the circulation of the right heart to the systemic circulation.

Anomalous pulmonary venous connection (or anomalous pulmonary venous drainage or anomalous pulmonary venous return) is a congenital defect of the pulmonary veins.

Left atrial enlargement (LAE) or left atrial dilation refers to enlargement of the left atrium (LA) of the heart, and is a form of cardiomegaly.

Scimitar syndrome, or congenital pulmonary venolobar syndrome, is a rare congenital heart defect characterized by anomalous venous return from the right lung (to the systemic venous drainage, rather than directly to the left atrium). This anomalous pulmonary venous return can be either partial (PAPVR) or total (TAPVR). The syndrome associated with PAPVR is more commonly known as "Scimitar syndrome" after the curvilinear pattern created on a chest radiograph by the pulmonary veins that drain to the inferior vena cava. This radiographic density often has the shape of a scimitar, a type of curved sword. The syndrome was first described by Catherine Neill in 1960.

It can result in many abnormal heart rhythms (arrhythmias), including sinus arrest, sinus node exit block, sinus bradycardia, and other types of bradycardia (slow heart rate).

Sick sinus syndrome may also be associated with tachycardias (fast heart rate) such as atrial tachycardia (PAT) and atrial fibrillation. Tachycardias that occur with sick sinus syndrome are characterized by a long pause after the tachycardia. Sick sinus syndrome is also associated with azygos continuation of interrupted inferior vena cava.

Inferior vena cava syndrome (IVCS) is a result of obstruction of the inferior vena cava. It can be caused by invasion or compression by a pathological process or by thrombosis in the vein itself. It can also occur during pregnancy.Pregnancy can lead to problems with blood return due to high venous pressure in the lower limbs, failure of blood return to the heart, decreased cardiac output due to obstructions in inferior vena cava, sudden rise in venous pressure which can lead to placental separation, and a decrease in renal function. All of these issues can arise from lying in the supine position during late pregnancy which can cause compression of the inferior vena cava. Symptoms of late pregnancy inferior vena cava syndrome consist of intense pain in the right hand side, muscle twitching, drop of blood pressure, and fluid retention.