What medical condition results in more fatalities in the U.S. than any other?

If you said heart disease, you got it right. According to the Centers for Disease Control and Prevention, nearly 600,000 Americans die each year due to cardiovascular disease, making it the leading cause of death in the U.S.

Now for some good news. Between 2000 and 2011, the number of deaths from heart disease and stroke has been reduced by 30%, largely because of improved medications. Even better, more than 200 new drugs are in development to treat these diseases. Here's one perhaps surprising company that is taking on America's most fatal disease.

Standing in the shadows
Gilead Sciences (NASDAQ:GILD) is known best for its blockbuster HIV/AIDS drugs. The company is also poised to soon emerge as a leader in the hepatitis C virus, or HCV, market. Gilead and AbbVie (NYSE:ABBV)are neck and neck in the race to launch the first all-oral HCV regimen. 

Source: Gilead Sciences. 

Standing in the shadows of these higher-profile products are Gilead's cardiovascular drugs Letairis and Ranexa. Pulmonary arterial hypertension drug Letairis generated more than $381 million in the first three quarters of 2013. Gilead holds U.S. rights to Letairis, while GlaxoSmithKline (NYSE:GSK) markets the drug outside the U.S. under the brand name Volibris. Ranexa, which is used to help control angina, brought in more than $318 million in the first three quarters. 

Even though both drugs have racked up success, they trail behind key rivals. Actelion's Tracleer is an endothelin receptor antagonist like Letairis. Sales for Tracleer in 2012 totaled $1.6 billion. Pfizer's (NYSE:PFE) angina drug Norvasc generated more than $1.3 billion in revenue last year. 

However, while both Tracleer and Norvasc are seeing declining revenue, Gilead is growing sales for both of its current cardiovascular drugs. Sales for Letairis jumped 29% year over year in the third quarter. Sales for Ranexa increased 22% last quarter compared to a year ago.

Waiting in the wings
Gilead sees even more opportunities for Ranexa. The company has three clinical trials in progress for the drug in treating other cardiovascular indications.

One late-stage study is exploring use of Ranexa in treating chronic angina patients with incomplete revascularization post-percutaneous coronary intervention. Gilead expects to complete this study in July 2014. Another phase 3 study relates to the use of the drug in treating coronary artery disease in patients with type 2 diabetes mellitis. Ranexa is also the focus of a mid-stage study targeting paroxysmal atrial fibrillation, a type of heart arrythmia.

Experimental drug GS-6615 is currently in an early-stage study for long QT syndrome. This disease is a rare genetic heart disorder that causes rapid and irregular heartbeats. 

A hearty stock pick?
Many heart disease patients are certainly being helped by Gilead's drugs that target heart disease and related conditions. Both Letairis and Ranexa continue to pick up steam and catch up with rival drugs from Actelion, Pfizer, and others. GS-6615 could add another arrow in Gilead's quiver down the road. Does all this mean that Gilead is a good stock pick solely as a result of its cardiovascular product lineup? I wouldn't quite go that far.

Cardiovascular still makes up less than 9% of Gilead's total sales. That percentage is growing, but maybe not for long. It's not that Gilead won't continue to see higher revenue from Letairis and Ranexa. It should. However, the company's all-oral HCV combo will likely be a much brighter star. Even if AbbVie squeaks by and reaches the market first, HCV looks to be a massive market for both companies (and others, for that matter).

The nice thing is that investors don't have to pick a stock based on just part of its portfolio. Gilead continues to be a juggernaut in the HIV/AIDS arena. The HCV market could be a game changer. And the company is still going after the nation's leading killer. Good news for patients -- and great news for investors.