Ventricular Septal Defect

Chai is a 7 months old Male Mongrel diagnosed with a grade III/VI systolic heart murmur during routine consultation. He was presented for a check prior to considering desexing surgery.


There is presence of a high membranous ventricular septal defect, just cranial to the aortic valves. VSD flow velocity from left to right is 5.5 M/S.

VSD is a relatively common defect in the cat, but uncommon in the dog.  VSD is a malformation of the interventricular septum, which allows blood to flow from the left side to the right side (high to low pressure). This causes volume overload of the pulmonary circulation, left atrial and left ventricular dilation and can result in left sided heart failure. Clinical signs vary on the size of the defect. With small (“ resisitive”) defects, patients are asymptomatic except for a loud harsh (typically right sided) systolic murmur and may have a normal quality and length of life.

With large (“ non- resistive”) defects, the heart murmur may be softer, but clinical signs related to pulmonary over circulation may develop, such as left sided heart failure or pulmonary hypertension. If pulmonary hypertension is severe enough to result in reversal of blood flow from the right to the left ventricle, cyanosis will occur. This is referred as “ Eisenmenger: s syndrome”. Treatment of this is similar to right- to left shunting PDA.

Echocardiography is used to visualize the defect (if large) and Doppler is used to assess blood flow through the VSD. Dilation of the left atrium and left ventricle can also be assessed, although this can also been observed on thoracic radiography, along with the absence of pulmonary over circulation and pulmonary edema.

Therapy depends upon the size of the VSD. If the defect is small, no therapy is required as a normal full life can be expected. Otherwise, the treatment is usually restricted to managing signs of heart failure or cyanosis if present. Closure with obstructive device might be possible and referral to a board certified cardiologist for management is always a reasonable option for congenital heart defects.