Washington DC - South Carolina Senator Lindsey Graham's sudden cause of death was revealed in preliminary findings released by the Washington DC medical examiner's office.

Graham's office on Sunday confirmed the senator died of a rare cardiovascular condition, but said the Washington DC medical examiner's office will not be definitive until all toxicological and microscopic testing is complete.

Taylor Reidy, the South Carolina senator's communication director, wrote on X that the preliminary examination defined Graham's cause of death as an "Aortic Dissection due to Arteriosclerotic Cardiovascular Disease."

An aortic dissection is when the innermost layer of the main artery tears, allowing blood to be pumped between its walls. This causes a sudden block of blood flow to vital organs and can also burst the aorta, triggering severe internal bleeding.

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"The death certificate will be PENDING until all the toxicological and microscopic testing are finalized and at that point the death certificate will be updated to reflect the cause of death and appropriately classify the manner of death," Reidy wrote.

Graham's potential cause of death came a day after emergency services were called to a report of cardiac arrest at his Capitol Hill home at around 8:30 PM on Saturday night.

Speaking to NBC News, a top staffer said the senator had been feeling generally unwell prior to his death. His office initially said Graham had died of "a brief and sudden illness" and requested his family be given privacy.

Graham had only returned from a trip to Kyiv, Ukraine, a few hours earlier, having met with Ukrainian President Volodymyr Zelensky on Friday.

"In honor of the remarkable life and achievements of Senator Lindsey Graham... I am ordering all American Flags throughout the United States lowered to Half Mast until Saturday evening at 6," said President Donald Trump in a post to Truth Social.