Cisplatin is one of the most common chemotherapy drugs used to treat many different cancers, including germ cell tumors (GCT). Cisplatin is very effective in treating GCT, but there are side effects. One of the possible long-term side effects of cisplatin is thought to be heart disease. The way that cisplatin causes heart disease is not well understood. One possibility is that cisplatin may damage the inside layer of blood vessels called the endothelium. The purpose of this study is to measure changes in the endothelium that happen when patients with GCT get cisplatin chemotherapy and to compare these changes with a group of patients not receiving chemotherapy.