Common signs of heart failure include enlargement of the heart (cardiomegaly) and fluid accumulation in the lungs (pulmonary edema), pleural cavity (pleural effusion), abdomen (ascites), legs (ankle edema), distended jugular veins, and liver (hepatomegaly). Locations for tissue sampling and sets of molecules for systematic studies of the molecular epidemiology of heart failure are indicated. Heart samples are obtained through endomyocardial biopsy (left section), from deceased donors, or donors undergoing heart transplantation. Plasma samples are obtained by centrifugation of blood from peripheral or central venipuncture. DNA for genome analysis can be isolated from any tissue, but most easily from leukocytes in blood samples. Microbial samples are obtained from urine, stool, genital, respiratory, skin, or oral swabs.