Heart disease, stroke, deep vein thrombosis and other diseases involving the circulatory system accounted for nearly 7 million hospital stays in 2004, according to a new report from the Agency for Healthcare Research and Quality. That represents about one in every six hospital stays, accounting for the greatest proportion of stays after pregnancy and childbirth. The most common circulatory diseases for which people were hospitalized were hardening of the arteries (1.2 million), heart failure (1.1 million), nonspecific chest pain (846,000), heart attack (695,000) and irregular heart beat (694,000).