"During an extreme bout of coughing, the patient spontaneously expectorated an intact cast of the right bronchial tree", the doctors' wrote.
Along with blood and mucus, he brought up a his left bronchial tree - a series of tubes that distribute air to his lungs.
During the week of his hospitalization the man's cough reportedly progressed to coughing up blood and phlegm.
While you can't actually cough up a whole human lung (you'll probably be slightly relieved to hear), as they're too large to fit through the trachea, you can apparently cough so violently that parts of your lung pop through the spaces between ribs.
The unidentified patient, whose case was written about in the New England Journal of Medicine, was receiving treatment at the University of California San Francisco (UCSF) Medical Center and had previously been fitted with a pacemaker.
It was originally folded in on itself, and the treating doctor, Georg Wieselthaler and his team carefully unfolded it, and were shocked at what they saw.
Though the clot is extremely unusual, it's not completely unheard of.
Blood clots are a known possible side effect of the pump. Doctors placed a ventricular assist device, a heart pump, into him to treat his condition, but he showed signs of respiratory distress.
"Blood clots may develop, which can travel through your blood vessels and block the blood flow to other organs, including your lungs making breathing hard", according to the Impella website.
After coughing up part of his lung, the patient was immediately intubated and doctors performed a bronchoscopy, which is a test that allows them to examine airways.
He also had to be supplied with oxygen due to breathing problems.
The patient later died from heart failure complications.
The man was reportedly "extubated" two days after the incident and suffered no further instances of coughing up blood.