Ventricular preexcitation in seven dogs and nine cats.

Ventricular preexcitation was diagnosed in 6 dogs and 7 cats examined because of weakness, syncope, or congestive heart failure, and as an incidental finding in 1 dog and 2 cats. Reciprocating tachycardias were documented in 8 of the cases. Six of the cats had a pathologic diagnosis of primary cardiomyopathy. Two of the dogs had an associated congenital heart defect. Reciprocating tachycardias were controlled in 4 cases with digoxin, in 2 cases with propranolol, and in 1 case with quinidine. Conduction through the accessory pathway was altered by quinidine (2 cases), digoxin, and propranolol (1 case each), resulting in a lengthened P-R interval and more normal QRS complex configuration.