More than 120,000 people need life-saving organ transplants, and each day 18 of them die waiting for one.

With the need outstripping the supply, doctors have to make tough decisions about who gets a new heart or liver and who does not.

Mark Johnson has four kids and has been married for 29 years. He has also been living with ventricular tachycardia, a rapid heartbeat that led to sudden deaths. But he always revived.

His wife, Lori, said he needed a new heart, and fast.

I just knew that he wasn't going to last much longer if he didn't receive a new heart, she said.

Johnson's doctor labeled him sickest of the sick.

Dr. Robert Higgins said, We kept him in the hospital until we could find the right heart based upon the blood type, the height and the weight.

A good organ match is only one of the criterion for getting a transplant. Other factors include the donor's proximity to the patient and the urgency of the situation.

Johnson said, It was a matter of waiting until you're sick enough to be on the list, but not so sick that the transplant's not going to help you. '

After four months, Dr. Higgins gave Johnson a new heart, a second chance. But, thousands on the list die waiting.

About 10,000 organ donors are available in the United States with more than 100,000 people waiting for life-saving, life-enhancing organ transplants.

With those odds, Johnson feels blessed.

Just being able to, you know, have a heart at this point is just beyond words, he said.

While organs are very much needed, Dr. Higgins said that tissue donation is just as critical. Donated corneas, skin and bone tissue can enhance even more lives.

The easiest way to sign up to be an organ donor is to sign up when you apply or renew a driver's license.

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