With a cloud hanging over its Lantus insulin, sanofi-aventis (NYSE:SNY) offered a ray of sunlight to investors this morning when the Food and Drug Administration approved its drug Multaq for restoring the heart's rhythm caused by atrial fibrillation.

The FDA approval, even with certain restrictions on Multaq's use, will mean a boost to revenue and morale for the French drugmaker. Its last major drug submission to the FDA – the weight loss drug Acomplia – was never approved.

In recent days, Lantus has come under criticism for an allegedly increased risk of cancer, although the statistical evidence is murky.

The FDA is examining the allegations that are based on a review of insurance records in four European countries. The company says the drug is safe.

The FDA's approval for Multaq gives CEO Chris Viehbacher something to build upon as he contemplates expanding sanofi-aventis' scope. Although he indicates the company won't act as dramatically as Pfizer (NYSE:PFE), which is buying Wyeth (NYSE:WYE), or Merck (NYSE:MRK), which is acquiring Schering-Plough (NYSE:SGP), Viehbacher says more generic-drug ventures are on the menu.

Measuring Multaq
It will be difficult to immediately assess Multaq's revenue potential due to the many degrees of severity of atrial fibrillation as well as the many treatments that include milder generic and brand-name drugs that slow down a rapid heartbeat, electrical jolts to the heart to restore normal rhythm, atrial pacemakers and surgery.

There's bound to be a growing market because the risk increases with age, according to the American Heart Association, which says about 2.2 million Americans have the disease. Atrial fibrillation, which is the quivering rather than the beating of the two upper chambers of the heart, is dangerous because it leads to the heart's inadequate pumping of blood. If blood coagulates and creates clots inside the heart and then is pumped out, the clots can block an artery and cause a stroke.

Multaq is approved for treating patients with atrial fibrillation and a companion condition called atrial flutter, and whose heart beats have returned to normal or who will undergo drug or electric-shock treatment to restore a normal rhythm. Sanofi-aventis will be banking on clinical trial results that showed the drug reduced cardiac hospitalization or death by 24% when compared to placebo.

This is heartening news for sanofi-aventis investors.

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Fool contributor Robert Steyer doesn't own shares of companies mentioned in this article. The Fool's disclosure policy's heart is all-a-flutter at this news.