For the entire time Dick Cheney was vice president, he had a secret letter of resignation pending.

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Dick Cheney, 72, suffered his first heart attack in 1978

In July 2010, Cheney made funeral plans with his family

While serving as vice president, he wrote a resignation letter

That letter was to be used if he became incapacitated

CNN  — 

Most have likely heard the broad outlines of the events that led to former Vice President Dick Cheney’s heart transplant: Five heart attacks, open heart surgery and a battery-operated heart pump.

But few are probably aware that the 72-year-old Cheney believed at one point he would not live through the night and made funeral plans with his family.

That’s just one of the surprising facts that I learned during an interview conducted over two days with the man widely considered to be one of the most powerful vice presidents in U.S. history. The interview is scheduled to air Sunday on CBS’ “60 Minutes.” It will air Tuesday on CNN.

Here are three things I learned during the interview:

1. He started smoking cigarettes when he was 12 years old, and his daily staple was a dozen doughnuts and three packs of cigarettes when he was President Gerald Ford’s chief of staff. He was just 34 years old.

Cheney suffered his first heart attack in 1978, at age 37, while he was campaigning for Congress.

It was the first of five heart attacks. He suffered subsequent heart attacks in 1984, 1988, 2000 and 2010. Cheney also underwent an open heart surgery and had a pacemaker implanted.

In June 2010, he was hospitalized for conditions related to his coronary artery disease. He had a Left Ventricular Assist Device, or LVAD, implanted to help his heart pump.

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2. In July 2010, he was convinced he was going to die. He made plans for his burial with his family, and then had a heart pump placed. That heart pump stayed in his body for 20 months until he got a heart transplant at age 71.

The LVAD, a battery-operated heart pump, is basically used to buy people time – a last resort, if you will – while they await a new heart.

Cheney waited 20 months for a transplant, twice as long as the average wait for a patient for a new heart.

3. For the entire time Cheney was vice president, he had a secret letter of resignation pending. He wrote this letter because he saw a gap in the U.S. Constitution. If a vice president is alive but incapacitated, there’s nothing in the Constitution that allows for that person’s removal. Worried that he might find himself in that position, he created the unprecedented letter.

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Cheney said he gave the letter to his counsel, David Addington, with instruction that it was to be delivered to President George W. Bush if Cheney were to become incapacitated.

Before Cheney accepted Bush’s offer to run as his vice president, he has said a team of doctors carried out a thorough evaluation of his heart.

After leaving office in 2009, Cheney’s appearance became increasingly frail.

I saw him a few years ago, and he looked so frail that I as a doctor thought the end was near for him.

Today, Cheney looks to be of normal weight and full of energy.

He is walking around with no shortness of breath, and he says he can do whatever he wants except ski.

That’s not because of Cheney’s heart. That’s because of his aging knees.

Dick Cheney: Fast Facts

CNN’s Chelsea J. Carter compiled this report.