It’s Valentine’s Day and so we put together a story for you about hearts – not candy hearts or even those filled with chocolate, but human hearts. These days, we know quite a bit about them. It’s been 50 years since the first successful transplant. But, in a way, hearts are also still full of mystery – and I’m not trying to get romantic on you. A doctor in Dallas is trying to solve those mysteries of the heart by studying the organs that no one wants anymore.

It’s cold and early. I’m at Baylor University Medical Center in Dallas with 85-year-old Dr. William Roberts. He’s lean, doesn’t have a lot of white hair left on his head and walks quickly. Hospital spokesperson Susan Hall tries to catch up to him as she asks about a recent vacation.

For almost 60 years, Roberts has traveled the country collecting the hearts of people who have had a transplant.

It’s an unusual thing to do because most doctors consider the old heart as waste.

But a handful – literally just four or five doctors around the world – study this waste. Roberts, right here in the heart of Texas, is one of them.

“There used to be quite a few people who did this,” Roberts says. “Now, I’m almost the only one left.”

For decades, Roberts has been fascinated by hearts and intrigued by transplants

But he wasn’t all that pumped-up by cardiology in general until he discovered that discarded hearts told stories. He says they tell him in detail how each patient lived – and hold the mysteries of why their hearts failed.

Like a detective, Roberts closely examines the scene. He looks at scars on each old heart, observing the size, the weight, the color.

We move into the lab where Robert’s assistant washes the heart Sandra Harvey was born with. Harvey is here, too. Now with a new heart, she looks gorgeous and healthy. Her skin is radiant. She sits at a round table near Roberts, who sounds like a medium reading Harvey’s cards.

Just from looking at her old heart, he correctly guesses her blood pressure, plus he notices that she must have spent years unable to lay down flat to sleep.

Roberts shows Harvey what a healthy heart should look like.

“Normally the left ventricle here is very small,” he says.

In the image, the left ventricle is closed tight, like puckered lips. But Harvey’s left ventricle looks like a wide-open mouth, unable to pucker.

Roberts draws on big sheets of paper to show Harvey how her heart was unable to pump blood. But what caused this? That’s still a mystery.

Often, the culprits are lack of exercise and an excess of food. Six million people in the U.S. suffer from heart disease – and the hearts in Roberts’ lab show it. They look like they were dipped in thick yellow wax, but actually they’re encapsulated in fat. They float in the buckets where Roberts stores them, which he says used to be rare.

“We did a study in 1983,” he says. “I believe only 5 percent of the hearts floated.”

Today, it’s about half.

But Sandra Harvey’s old heart is not one of them. It’s lean. She tells doctor Roberts she’s an Army veteran who exercised and ate well. Her mother was a nutritionist, but her mother suffered from heart failure, too, and died from it. Harvey wonders where things went wrong.

Roberts tells her she’s very lucky to have a new heart – out of millions waiting, only about 30,000 people get one every year – and she didn’t do anything wrong. He says the mystery in her case leads back to genes. Roberts says Harvey should stop dwelling in the past and focus on how much better her health is.

“Now, that I have a new heart, everything is fantastic,” Harvey says. “Even my hair is growing.”

“What’s the secret to that?” Roberts says.

We all look at Doctor Roberts’ bald head and laugh. How to grow hair is a mystery for some other time.

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Sandra Harvey’s heart at the Baylor Heart and Vascular Institute. Photo: Jorge Sanhueza-Lyon/KUT News