Double inlet left ventricle (DILV) includes hearts in which both atrioventricular (AV) valves are aligned with and connected to one ventricular chamber of left ventricular morphology.  One of the two AV valves may straddle the ventricular septum by greater than 50%. 
The AV valves are often recognizable as a tricuspid or mitral valve. The AV valve near the free wall can be of mitral valve morphology and the AV valve near the septal wall is more of tricuspid valve morphology.  However, in many instances of DILV, the AV valve anatomy is not sufficiently distinct to allow accurate differentiation of morphologic tricuspid or mitral valves.  Hypoplasia and stenosis of one AV valve is seen in up to 15–20%. Occasionally the AV valve near the septum straddles across the VSD into the small outlet chamber in 14% of cases.  
The left ventricular chamber has a free wall on one side with multiple papillary muscles and a smooth septal wall which is characteristic of the left ventricle.  The incomplete right ventricle (outlet chamber) is always carried on its antero-superior shoulder.  In left-handed ventricular topology or L-ventricular loop (65%), the smooth ventricular septum is anterior and leftward near the outlet chamber. In right-handed ventricular topology or D-ventricular loop (35%), it is anterior and rightward. There is often a large muscle bundle called the posterior median ridge on the inferior or diaphragmatic wall of the left ventricle, running from base to apex between the AV valves.
The ventricular septal defect (VSD) can be variable in position, number, and size. A small communication often results in obstruction to the outflow that arises from the outlet chamber.  
Transposition of the great arteries with left and anterior aorta (L-transposition) occurs in almost all DILV with left-handed ventricular topology (65% of DILV). In right-handed ventricular topology (35% of DILV), transposition with anterior and rightward aorta (D-transposition) accounts for 20%, and normally related great arteries (also referred to as a Holmes heart) accounts for 15%. 
Summary of Subtypes:
DILV with anterior and leftward aorta (l-looped ventricles/left-handed ventricular topology)
VSD provides communication to hypoplastic right ventricle
Subaortic obstruction can be associated with a restrictive VSD
DILV with normally related great arteries (D-looped/right-handed ventricular topology)
Also known as a Holmes Heart
Right sided hypoplastic subpulmonary incomplete/hypoplastic RV cavity
Left-sided morphologic left ventricle
VSD provides communication into hypoplastic right ventricle
VSD may be a substrate for subpulmonary obstruction which may to some degree be favorable and result in a balanced circulation
Others features/associated lesions:
Usual atrial arrangement (atrial situs solitus) with normal systemic and pulmonary venous connections are most commonly seen in DILV.
The atrial communication is usually small or intact.
Subvalvar obstruction of the posterior root, the one aligned with the left ventricle, usually the pulmonary artery, can be due to posterior malalignment of the outlet septum, AV valve tissue, or a fibromuscular ridge.
Subaortic stenosis and often hypoplasia of the aorta with coarctation or even arch interruption can occur. The aortic arch is usually left-sided and branching is usually normal.
The branch pulmonary arteries are usually confluent and of normal caliber, even in cases of subvalvar and/or valvar pulmonary stenosis.
 S. P. Sanders, “Hearts with Functionally One Ventricle,” in Echocardiography in Pediatric and Congenital Heart Disease: From Fetus to Adult: Second Edition, 2nd ed., W. W. Lai, L. L. Mertens, M. S. Cohen, and T. Geva, Eds. WILEY Blackwell, 2016, pp. 509–540.
 M. G. Earing, D. J. Hagler, and W. D. Edwards, “Univentricular atrioventricular connection,” in Moss & Adams’ Heart Disease in Infants, Children, and Adolescents, Including the Fetus and Young Adult, 9th ed., H. D. Allen, R. E. Shaddy, D. J. Penny, T. F. Feltes, and F. Cetta, Eds. Lippincott Williams & Wilkins, 2016.
 D. J. Penny and R. H. Anderson, “Other Forms of Functionally Univentricular Hearts,” in Paediatric Cardiology, 3rd ed., R. H. Anderson, E. J. Baker, D. J. Penny, A. N. Redington, M. L. Rigby, and G. Wernovsky, Eds. Churchill Livingston, 2010.
 M. Bevilacqua, S. P. Sanders, S. Van Praagh, S. D. Colan, and I. Parness, “Double-inlet single left ventricle: Echocardiographic anatomy with emphasis on the morphology of the atrioventricular valves and ventricular septal defect,” J. Am. Coll. Cardiol., vol. 18, no. 2, pp. 559–568, 1991.