Don Ho isn't worried about how his heart will respond when he returns to the stage Sunday night in Waikiki.

It's his voice that concerns him.

"I don't know if I can sing," said Ho, 75, who underwent an experimental stem cell procedure last month in Thailand to bolster his heart muscles. "My stamina's good. I don't want to sit around and do nothing, which is why I've been trying to clean out some junk at home. But I just don't know how my voice is going to sound."

Ho long has been Hawai'i's most recognized entertainer. His experimental surgery on Dec. 5 generated headlines worldwide and gave hope to others with failing hearts.

Sunday's performance, which will include his trademark "Tiny Bubbles," will be the latest step toward resumption of routine as his heart continues to improve.

"Just going back to work will be great," he said. "We'll start with one show and see how that goes."

Ho said he hasn't practiced or tried to reaccustom his vocal cords by doing scales since the surgery. That's because his condition — cardiomyopathy, a serious disease in which the heart muscle becomes inflamed and does not function normally — had left him breathless, even woozy. At its worst, he could not complete singing in his show.

"I had no hope before I had the surgery," he said. "There was nothing else out there; so I had to do it."

The ticker has not failed him since the procedure. "The shortness of breath is history," he said.

Yesterday, he wore a baseball cap with "E'ola" embroidered on it. "It's a Samoan word that means 'to give life,' " said Ho, his face leaner than a year ago, his smile broader because of his swift recovery.

HOW STEM CELLS HELPED

The experimental stem cell therapy procedure is still under review in the U.S. It involves an injection of stem cells derived from the patient's own blood. The stem cells are isolated, then multiplied, through a patented laboratory process conducted in Israel, and then inserted directly into the heart or arteries to help restore damaged tissue.

The procedure regulates the patient's heartbeat and improves the heart.

Ho said that by watching his diet and exercising lightly, his recovery has been remarkably smooth.

"They tell me to watch what to eat," he said. "So I have cereal, some eggs every other day, and a lot of salads — with only little dressing."

He can't take on stressful exercise — "no lifting heavy things" — but walking has been his panacea.

"I walk 20 minutes, twice a day. No treadmill. No bicycle. Just a simple walk. Me, I walk around the bed. Walking also has strengthened my legs, which means my heart doesn't get overworked."

Ho has lost about 20 pounds since the surgery and weighs between 180 and 185.

"My weight when I played high school football was 140," said the Kamehameha graduate. "If I can get down to 175, I'd be happy."

Ho said that cardiothoracic surgeon Dr. Kitipan Visudharom — "I call him Dr. Kit, and he's a sweetheart," Ho said — performed the procedure at the Bangkok Heart Hospital, under the supervision of Dr. Amit Patel of Pittsburgh, who helped arrange the surgery in Thailand. Because the therapy is not approved by the Food and Drug Administration, it has to be done outside of the U.S.

"There were six in our group to have the procedure," Ho said. "They do two procedures a day."

Patel was in the Islands recently to consult with Ho and check on his recuperation.

Ho said that before the procedure, he was told his heart was operating at about one-third its capacity.

"Everybody thought I had 30 percent of my heart left, but Dr. Patel said that it really was down to 10 percent. So, in retrospect, I had to do this. Pretty soon, I think I will be up to 50, maybe 75 percent capacity. Takes six months."

He still relies on a pacemaker and fibrillator "but this stem cell thing has leveled off the whole body; I had my vitals checked before I left, and there were indications that there was disintegration of my liver, my kidney; blew me away, because now, everything's perfect."

NO MORE WINE

There's a lilt, and apparent joy, in Ho's voice now. "I feel lucky, I feel grateful," he said. "I don't drink wine anymore; I think I was punished for all the fun I had when I was younger. I've not had a bad day, really, since returning home. I know my voice is a little stronger now than before the surgery."

He said anyone with signals of irregular heartbeat — he had about a dozen episodes before he explored the surgery — should pay attention to warnings. "And I recommend everyone to start walking — best way you can help your heart."

But it worries him that he doesn't know how he'll sound when he returns to Waikiki stage for the first time.

"That's why I'm surrounding myself with the kids," he said of his cast of young talent, including an 'ukulele player, a karaoke contest winner, a singer and more.

"Our style always has been variety."

Reach Wayne Harada at wharada@honoluluadvertiser.com.