One of the first sights upon passing through the massive double doors at the Mill Neck mansion known as Frost Mill Manor is a Murano glass chandelier. Its color -- red -- is an ode to the occasion for opening this 1928, seven-plus-bedroom home to the public: The Home Is Where the Heart Is Designer Showhouse, which starts today, is a decorator's dream benefit for the Long Island Chapter of the American Heart Association.

"When you walk in, you want to have a 'wow,' " says Kim Radovich, one of the chapter's board chairs who is serving as design chair of the event. The Huntington Bay designer, one of more than two dozen whose work is featured at the event, hung the 42-inch chandelier by a winding staircase she covered with a bold cheetah carpet as a tone setter for the rambling rooms that follow.

But what won't be seen may be just as astonishing. Designers say they walked into a Gold Coast gem of a home, the site of a show house in the past, in need of repair. Not only was an original toilet "leaking and smelly" in the now glamorous and gleaming powder room off the grand entrance, but there were mustard and gold upholstered walls covering layers of old wallpaper. "It took days to take it all down," says designer Christine Gentile of Ashbourne in Centerport, who installed marble floors and molding.

While looking over Gentile's handiwork, make sure to peek inside the washroom to see what a $2,000 faucet looks like. It is one of many designer touches to behold.

UPTOWN, DOWNTOWN

"I wanted this room to envelope you, like a big hug," says Port Washington designer Keith Baltimore of his space. That hug might feel like it's from someone who's a little off -- the grand first-floor space looks more like a Brooklyn loft than a Gold Coast living room. Broad black and white horizontal stripes encase the 35-by-40-foot area, which is accented brightly with red and blue furnishings. Look for tucked-away, whimsical surprises such as the half-peeled gold ceramic banana in the pediment above the door.

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DIY TIP: If you like the look of the stripes, try them at home, says Baltimore. "The larger they are, the less busy they look," he adds. He suggests painting one stripe with flat paint and the other with gloss paint to create "an interesting effect." But keep in mind: Small pieces of furniture look better against larger stripes, he says.

A SPACE OF THEIR OWN

The inspiration for Merrick designer Rose Ott's sage and taupe bedroom came from the hand-painted French furniture. Two stuffed animals, a small table with teacups and tiny dressy dresses hanging about are among the few clues that the space is meant for a child. "Kids are so overwhelmed by technology and noise that they need to have a place to be quiet but still play," she says.

DIY TIP: When it comes to decorating a bedroom for a little one, Ott suggests simplifying the task. "Don't overload it and cram it with too much stuff," says Ott. She had started to hang gilded flowers on the walls, but decided to keep them bare.

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This is the second time Manhasset designer Denise Rinfret has decorated the mansion's wood-paneled library, but her first effort 15 years ago was very different. Then, it centered around a 60-inch flat-screen television that looped a movie for visitors coming for a peek. It was more a media room than a place where one might go to read, she says, pointing out that a computer system atop a partners desk in front of arched French doors overlooking the property controlled the room's electronic bells and whistles. This time around, Rinfret says, she "went with the richness of the room," restoring the walnut walls and opting for soft, gentle music instead of blaring Hollywood surround sound.

DIY TIP: Rinfret, whose firm The Rinfret Group with Missy Rinfret Minicucci also has an office in Manhattan, says that every home should have a space just for reading, quiet conversation, meditation. "Rooms should be an inspiration for your thoughts," she says.

PULL UP A STOOL

The seating in Huntington designer Katharine Posillico McGowan's breakfast room is probably not like any you're used to seeing around the table -- there's a banquette, plastic bistro chairs, stools with upholstered tops.

DIY TIP: The space also includes a mudroom and a makeshift beverage bar, but an eat-in kitchen of any size can accommodate an imaginative seating setup. "The idea is to mix unexpected things together -- use things you would normally use in your living room," says McGowan, who owns Katharine Jessica Interior Design.

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HITTING THE WALL

Instead of a headboard, Bellmore designer Rachel Florez constructed a 13-foot-wide, 8-foot-high wall, constructed in pieces, behind the bed in the second-floor guest room she decorated. The wall looks like it's been covered with glass tile, but it's actually Hartmann & Forbes wallpaper made of abacá, a banana plant harvested for its fiber, with metallic thread. There is a recessed area for the bed. "The wall gives the bed a focal point and defines the space," Florez says.

DIY TIP: Florez says that such a wall can be constructed for any size room with Sheetrock and 2-by-4s. "You can paint it, you can tile it, you can paper it, you can upholster it," she says.

BELLY UP INSIDE

Sea Cliff designer Margreet Cevasco turned a cramped room off the main entrance into a bar -- by building a niche into one of the walls. Lit with fixtures hand-forged by her son Chris Zeppieri and his business partner Ryden Rizzo's company, Glen Cove's Allied Maker, the recess is intended for mixing and serving drinks. A mirrored back widens the space. Two oversized, chaneled, armless chairs around a fireplace with a painting on top face the bar. The room is only 10 by 11 feet. "I love the idea that it's small and intimate," she says.

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DIY TIP: Constructing a recess to create a bar like this one may not only be too costly but impossible, so try installing a floating shelf instead, says Cevasco. Hang a mirror with a light over it, she suggests.

BRIGHT AND AIRY

As if the sun porch doesn't shine enough with its brass sputnik light fixture, bar cart and wall mirror, Manhattan designer Melanie Roy placed a gleaming 18-karat gold Harry Bertoia side chair in one corner. "It's a fresh take on an old classic, which is what I tried to do in this room," says Roy, who has a home in Bridgehampton. Other touches -- from a custom-made sofa to a honeycomb table -- update the space with its exposed brick walls and intricate metalwork.

DIY TIP: Although the room provides wide-open views of a corner of the grounds, Roy brings nature into the space. Oversized planters contain boxwoods, a large ottoman contains a palm tree in the middle, and there's a table made of driftwood.

About Frost Hill Manor

Frost Mill Manor was built in 1928 for Olympic skater Irving Brokaw, who was also an artist and lawyer. His once-expansive grounds, sections of which have been sold off throughout the years, were designed by the Olmsted Brothers, best known for Central Park.

Now on almost 6 acres, the home and its property is expected to be put on the market next week for about $7 million, says Chris Smithers, 47, president of the nonprofit Christopher D. Smithers Foundation, a major supporter of the Long Island Council on Alcoholism and Drug Dependence. The foundation, named after Smithers' grandfather, uses the third floor of the house for offices.

"We've done tons of work," says Smithers, pointing out that the kitchen and grounds have been redone.

Proceeds from the sale of the house -- which Smithers' father bequethed to the foundation -- will support efforts to raise funds to treat alcoholism.

WHAT: Home Is Where the Heart Is Designer Showhouse, a benefit for the Long Island Chapter of the American Heart Association

WHEN / WHERE: 10 a.m. to 4 p.m. Tuesdays through Fridays and 11 a.m. to 5 p.m. Saturdays and Sundays, starting today and closed Mondays, through May 31, at 393 Oyster Bay Rd., Mill Neck

INFO: $35, which includes a show house journal; no admission 30 minutes before closing; no strollers, infants, children under 6 or pets admitted; 516-723-9370, americanheartshowhouse.com