The emergency technicians burst through the doors, pushing a stretcher into the crowded E.R. Their walkie-talkies dangled from their shoulders, squawking and hissing like demented parrots. The triage nurse directed them straight into a room as the E.M.T.’s barked out what they knew. “Sixty-four-year-old man . . . history of a stroke . . . complaints of weakness and belly pain.” His heart was slow, they reported; his blood pressure so low that it was immeasurable. The monitor showed a heart rate in the 20s — normal is over 60. Dr. Bernd Woerner strode in and quickly assessed the situation. “Get me an amp of atropine,” he snapped, calling for the medicine used to speed up the heart.

The doctor watched as the monitor screen continued its flat yellow line, broken only occasionally by the spike indicating another heartbeat. Slowly the patient’s heart rate and blood pressure began to rise.

Throughout all this the patient was alert, Woerner told me later. He explained to the patient, “Your heart is pumping too slowly.” The medicine would keep his heart rate up until the cardiologist arrived in an hour or so to insert a pacemaker. In the meantime, they had to begin to figure out what was wrong with his heart.

I knew this patient. I was his internist and had been seeing him for the past year, since he had his stroke. Before that, he hadn’t been to a doctor for decades. He came to me when the massive stroke rendered his right leg and arm nearly motionless, his face crooked and his speech slurred. Still, his beautiful cockeyed smile and gallant manner made him a favorite at our office. He often brought us gifts — candy or some of the pecans sent from his family in North Carolina. He was doing well, so I was shocked when I got word from the E.R. that my patient was dying. And the doctors there weren’t sure why.

With the usual chaos of the emergency room boiling around them, Woerner forced himself to sit quietly as the patient described his symptoms. The man spoke in an unnaturally deliberate drawl, as if in slow motion: “I — can’t — walk.” It started the night before. He felt weak, could barely move. Any chest pain? Woerner broke in. Shortness of breath? Fever or chills? Vomiting? The patient shook his head no. He was taking medications to lower his blood pressure and cholesterol. He had not smoked or drunk alcohol since his stroke. Examining him, Woerner saw the results of the stroke but little more.

2. Investigation

Why was his heart beating so slowly? the doctor wondered. Had he taken too much of one of his medications? Had he suffered a heart attack that affected the natural pacemaker in his heart?

Part of the answer came less than an hour later. The lab called to report that the patient’s kidneys weren’t working. And his potassium — an essential element in body chemistry, regulated by the kidneys — was dangerously high. Potassium controls how easily a cell responds to the body’s commands. Too little potassium, and the cells overreact to any stimulation; too much, and the body slows down. The patient was given a medicine to get the potassium out of his system and then transferred to the I.C.U. for monitoring.

If the potassium was high because of his kidney failure, what had caused his kidneys to fail? Dr. Perry Smith, the intern on call in the I.C.U., gnawed at this question as he reviewed the chart and examined the patient. It wasn’t a drug error. The patient’s medication box showed the correct number of pills. And it hadn’t been a heart attack; a blood test proved that. Smith looked for the results of the urinalysis to see if there was any clue there. Somehow no one had sent any urine to the lab. Were his kidneys too damaged to produce urine? That would be important to know. Smith asked the nurse to get some urine from the patient.

She returned empty-handed. The patient couldn’t urinate, and she hadn’t been able to insert a Foley catheter, a rubber tube that is passed through the urethra into the bladder to collect urine. Was something blocking the urethra? A urology resident finally managed to get a catheter into the bladder. Urine gushed out — nearly half a gallon of it. A full bladder normally holds only a quarter of that. The urology resident looked at the intern: “I guess now we know why his kidneys weren’t working.”

3. Resolution

The urethra was blocked — by the prostate gland. The prostate surrounds the urethra, and when it enlarges, as it often does with age, it impinges on the narrow outlet, obstructing and ultimately blocking it so that no urine can pass. As the trapped liquid filled the bladder, the pressure shut down the patient’s kidneys.

Just hours after the obstruction was relieved, his potassium began to drop as the kidneys went back to work. Four hours later, the patient’s heart rate was up over 60. By the next morning, the abdominal pain, probably caused by his hugely distended bladder, had eased. When he left the hospital three days later, his potassium and heart rate were normal and his kidneys, nearly so. He would have to keep the tube in his bladder until his prostate could be removed.