Natalie Cole's family says the singer's cause of death was heart failure brought on by a rare lung disease. After Cole received a kidney transplant in 2009, she was diagnosed with pulmonary arterial hypertension, a disease that causes shortness of breath, dizziness, and sometimes chest pain, her family said in a statement to the AP. Cole "responded well to pulmonary arterial hypertension-specific agents over many years, during which she performed many concerts world-wide, but eventually succumbed to intractable right heart failure, an outcome that unfortunately commonly occurs in this progressive disorder," the statement reads. Cole had battled drug problems and hepatitis that forced her to undergo the 2009 kidney transplant. (More Natalie Cole stories.)