Natalie Cole's family said the singer's cause of death was idiopathic pulmonary arterial hypertension, which led to heart failure.
Her family said in a statement to The Associated Press on Thursday that after Cole received a kidney transplant in 2009, she was diagnosed with pulmonary arterial hypertension, a rare lung disease that causes shortness of breath, dizziness and sometimes chest pain. Because Cole's case was idiopathic, the exact cause is unknown.
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The statement read: "(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."
Cole died last week. She had battled drug problems and hepatitis that forced her to undergo a kidney transplant.