Excessive alcohol consumption is known to cause weakness of the heart muscle, a condition called cardiomyopathy. However, because not all alcoholic persons develop cardiomyopathy, some researchers have suggested that a person's risk for this complication depends on his or her genetic make-up. Packets of genetic material, known as genes, occur in pairs, and each parent contributes half of the pair to the child. Although genes from each parent may be identical, they often differ slightly—these variations are called alleles. Alleles can lead to slight variations in the chemicals produced by heart muscle tissue. One chemical suspected of having a role in alcoholic cardiomyopathy is angiotensin-converting enzyme (ACE). Because of the occurrence of different ACE alleles, different forms of ACE can be present in cardiac muscle. These forms of ACE can be identified in a laboratory.