Sen. Bernie Sanders (I-Vt.) on Sunday backpedaled on his promise to release comprehensive medical records, saying his doctors have confirmed hes in good health.

You can start releasing medical records it never ends, Sanders told NBCs Meet The Press when asked whether he planned to release additional medical records after having a heart attack in October.

We have released a substantive part of all of our background, he added. We have doctors who are cardiologists who are confirming that I am in good health. I am in good health.

The 78-year-old Democratic presidential hopeful said in September that he would absolutely release his medical records ahead of the presidential primary season, which kicked off with the Iowa caucuses last week.

The American people have the right to know whether the person theyre going to be voting for for president is healthy, Sanders said at the time. And we will certainly release our medical records ... before the first votes are cast.

Sanders echoed his vow a few weeks after his Oct. 1 heart attack, telling The Associated Press that he planned to release comprehensive medical records by the end of the year.

He released three brief letters from his doctors one primary care physician and two cardiologists in December that declared he was in good health currently, but he has not released his full medical records.

Meet The Press host Chuck Todd asked Sanders on Sunday whether voters should be able to see his full medical records before Super Tuesday, which is on March 3.

We have released as much documentation I think as any other candidate, Sanders said.

But some of his fellow Democratic presidential contenders have released more detailed summaries of their records and, in some cases, results from various medical tests and procedures.

Sen. Elizabeth Warren (D-Mass.) was the first Democratic presidential candidate to release personal medical records. The documents provided by her campaign in early December included a doctors note, which declared the candidate in excellent health, as well as a two-page hematology report and a three-page chemistry report.

Former Vice President Joe Biden also released a doctors report in December, which outlined his surgical history and his current medical conditions.

When Sanders pushed back on releasing additional medical records Sunday, Todd noted that hes the only candidate who has had a heart attack.

Well, look ... no other candidate is doing four or five events a day running all over this country, Sanders replied. Sanders, of course, isnt the only candidate with a busy schedule on the campaign trail. Most of his rivals are participating in several events each day.

When asked what changes his doctors had recommended following his heart attack, Sanders said he has been told walk and sleep more.

I am trying to walk a little bit more, but the schedule doesnt allow me, he said. Were trying to sleep a little bit better. Sometimes thats hard. But Im feeling great.

He added that winning the election would help him sleep a lot better.

A representative for Sanders campaign did not immediately respond to HuffPosts request for comment.

Read the three letters released from Sanders doctors in December below: