Highest maternal moality is seen in following congenital hea disease:

Eisenmenger's syndrome is the reversal of a left to right shunt (ASD, VSD, PDA) due to progressive pulmonary hypeension. Right to left shunting leads to systemic aerial oxygen desaturation and central cyanosis. The degree of cyanosis is determined by the extent of pulmonary vascular obstructive disease. Maternal moality approaches 30-50% and fetal loss may be as high as 75%. It is one of the few conditions in which pregnancy is contraindicated. Maternal moality rates average 3 percent in coarctation of aoa. Maternal moality increases in VSD when there is reversal or bidirectional flow--Eisenmenger syndrome. Maternal moality rates approach 10 percent in pulmonic stenosis. Ref: Hameed A.B., Montoro M.N. (2013). Chapter 27. Cardiac & Pulmonary Disorders in Pregnancy. In A.H. DeCherney, L. Nathan, N. Laufer, A.S. Roman (Eds), CURRENT Diagnosis & Treatment: Obstetrics & Gynecology, 11e.