PARIS — Tanya Heath is on a double mission: to prove women can wear heels without ruining their feet, and that her answer to their plight, a heel that switches from high to low, can be made entirely in France.

The Paris-based Canadian started with a simple idea. When your shoes start to hurt - half way through a party, a wedding or a workday - press a button in the sole, slot out your dressy high heel and replace it with a walking version.

"I'm a feminine feminist," is how the 42-year-old sums up her philosophy. "My shoe is designed to be sexy - but on the woman's terms."

"You can do your two-hour meeting, and then you just take off your high heel," she explained at the Ethical Fashion Show in Paris this month. "You're getting relief - and you're getting home."

So far so good, except the trick - which no one had quite figured out until now - is how to keep the shoe balanced and comfortable both on tip-toe and when you tilt it back to sit on a low heel.

Fruit of three painstaking years of research, Heath's patented answer to the riddle is billed as the world's first multi-height heel, a luxury leather shoe that switches seamlessly from nine to four centimetres (3.5 to 1.5 inches).

From pastel pink patent sandals to strappy dancing shoes or demure lace-ups, with either stiletto or chunky heels, high or low, the shoes are pitched at the high end of the market, starting at around 250 euros (320 dollars).

With models harking back to the 1920s, Heath wanted a "deliberately nostalgic" style to offset the "gee-whizz technology".

"It's an incredible game of geometry," she said. "All shoes, quality ones, follow a set of geometric rules, and always have done. I don't follow those rules. We did things differently."