Heart cancer can develop in any part of the heart, with angiosarcomas being the most common type in adults. The cause of heart cancer is unknown but involves changes in heart cells that lead to uncontrolled growth. Initial symptoms of heart cancer may be vague like chest pain or pressure, but can worsen to include bluish skin, confusion, difficulty breathing, or an irregular heartbeat. While the outlook is serious if left untreated, complementary therapies like acupuncture, massage, and yoga may help support people undergoing treatment for heart cancer.