An inherited form of heart muscle disease where the heart ventricles become dilated which affects the hearts ability to function normally. The disorder is caused by the degeneration of the hearts conduction system. Type 3B is caused by a defect in the dystrophin gene on chromosome Xp21.2. Males tend to be more severely affected than males with death occurring within about a year from the onset of symptoms. Symptoms in males tend to occur by the age of 21 and females tended to have an onset during their fifth decade of life with a relatively slower course of progression than in males. See also Cardiomyopathy dilated 3B