Subvalvular aortic stenosis is an abnormality of the subaortic region currently classified as a non-cyanotic congenital heart malformation that causes the partial obstruction of the left ventricle outflow tract. This condition has a progressive and recurrent character.
Subvalvular aortic stenosis is more frequently seen in males  and may be asymptomatic during the early childhood. In this case, it is incidentally discovered during a heart murmur evaluation . Symptoms tend to occur as the patient grows older  and the lesion becomes more severe. Initially, the patient comes with complaints that only install during physical efforts, such as dyspnea, dizziness, presyncope or angina with normal coronary arteries. In more advanced stages, veritable syncope is caused by less intense effort. Additional complaints include orthopnea and other heart failure manifestations. Sudden cardiac death may be the first sign of disease. Orthopnea may signify the presence of pulmonary venous hypertension, while syncope may be due to an arrhythmia, as well.
The stature and ponderal growth of affected children are normal. In cases with other heart malformations, like a ventricular septal defect, patent ductus arteriosus, pulmonic stenosis or aortic coarctation , the physical evaluation may fail to raise subvalvular aortic stenosis suspicion. Jugular inspection reveals a prominent "a" wave, caused by decreased compliance of the right ventricle. Arterial pulses are symmetrical and seldom decreased. Carotid palpation may prove the presence of an arterial thrill, while a precordial thrill may be felt upon palpation of this area. The apical impulse is strong. Auscultation highlights the existence of a narrow or paradoxical split second heart sound, associated with an ejection murmur, best heard in the middle left sternal border, radiating to the upper left border of the sternum, with a longer duration if the obstruction is more severe. The physician can differentiate this murmur from that of valvular aortic stenosis based on the absence of clicks. Other murmurs, like that of aortic or mitral regurgitations, sometimes coexist.
Given that pure subvalvular aortic stenosis is a non-cyanotic congenital heart malformation, blood workup is usually noncontributory. The electrocardiogram depicts the degree of underlying left ventricular hypertrophy in most patients. The strain pattern, as well precordial deep Q waves are rarely seen.
Echocardiography is the diagnostic method of choice. This imaging is able to describe the shape of the left ventricular outflow tract, the degree of obstruction, the existence of associated congenital abnormalities, like aortic coarctation or patent ductus arteriosus  and disease consequences . The color doppler probe placed in the left ventricular outflow tract reveals a turbulent flow , the first obstruction indicator. The M-mode cursor put in the same area demonstrates the presence of early closure and flutter of the aortic valve leaflets. It is important to characterize the length and position of the lesions and their relationship with the mitral and aortic valves and this is done using parasternal, apical and subcostal views. The gravity of the disease is assessed by continuous doppler wave interrogation, based on mean pressure gradient across the left ventricle outflow tract. However, this is not a reliable method in tunnel-like or multiple lesions. In these cases, a cardiac catheterization with pullback pressure measurement is needed.
The echocardiography should be performed several times in order to observe disease progression, to characterize left and right ventricular filling and function and the impact of the condition on the aortic valve in terms of regurgitation  . In cases where the acoustic window is poor, diagnosis is aided by transesophageal echocardiography. This is most useful in severe, symptomatic patients that are going to be referred for surgery . Supplementary information, like the severity of mitral regurgitation, the existence of ventricular septal defects or the exact anatomy of the left ventricle is offered by a left ventriculogram.