The unnamed patient was being treated at the intensive care unit at the University of California San Francisco Medical Centre, which was where reports say he started coughing violently.
Doctors working at the hospital said the man instantly felt better after coughing up the clot but the size of it suggested the 36-year-old's condition was severe.
Doctors are bewildered as to how an extraordinarily shaped blood clot came out of a patient.
"An Impella ventricular assist device was placed for management of acute heart failure, and a continuous heparin infusion was initiated for systemic anticoagulation".
The patient had a pacemaker fitted due to a history of poor cardiovascular health, according to the New England Journal of Medicine.More news: Stocks drop as falling United States yields, trade worries hit mood
In 2012, it was reported a 40-year-old in the United Kingdom literally coughed out her lung through her ribs.
Doctors were surprised by the blood clot cast.
The man coughed up the right bronchial tree.
The pulmonary surgeon Dr Georg Wieselthaler told The Atlantic when he carefully spread out the clot, realising it was the flawless shape, he was "astonished".
The New England Journal of Medicine (NEJM) posted a picture on Twitter of a coughed up blood clot in the shape of a patient's right lung's bronchial tree.More news: Jennifer Aniston Opens Up About Her Marriages & Having Children!
"We were astonished", Dr Wieselthaler said.
The man died from heart complications a week after coughing up the clot.
The 25-year-old mum went on to recover fully and delivered a healthy, full-term baby soon after.
Wieselthaler called the occurrence "very, very, very rare".
The right bronchial tree consists of three segmental branches in the upper lobe (blue arrows), two segmental branches in the middle lobe (white arrows), and five segmental branches in the lower lobe (black arrows).More news: Yemeni talks to start Thursday in Sweden: Houthi leader