If I drank alcohol during my pregnancy, can that cause cardiomyopathy in my child?

Unlikely. Amoung the original children reported with fetal alcohol syndrome the heart issues were discribed as transient murmurs or vsd(hole between lower chambers).A dose relatred effect was seen in the syndrome and many of these mothers succomed to etoh disease within a year. For cardiomyopathy you are more likely looking at acquired viral infections or rare inherited metabolic disorders (with other pbs).
Alcohol . If you drink alcohol during pregnancy, not only there is risk of cardiomyopathy in your baby, but there is a risk of fetal alcohol syndrome, developmental disabilities, mental retardation risk too. In addition, the risk for adhd is much higher.