Merck & Co Inc said on Monday its experimental therapy helped increase exercise capacity in patients with a deadly disease that causes high pressure in blood vessels of the heart and lungs in a late-stage study, lifting its shares about 4%.

Sotatercept, combined with a background therapy, helped patients with pulmonary arterial hypertension to walk about 40.8 meters more in six minutes.

The drug, which Merck gained through its $11.5 billion buyout of Acceleron Pharma in 2021, also showed significant improvement in eight of the nine secondary goals, including reducing the risk of death or clinical worsening of condition by 84% compared to placebo.

J.P. Morgan analyst Chris Schott said the data exceeded the brokerage's expectations and "should confirm the drug as go-to add-on therapy" for pulmonary arterial hypertension.

Schott forecast peak sales of $3 billion to $4 billion for the drug.

In October, Merck said sotatercept had met the main goal of a late-stage study, but did not release the full data.

Merck has been beefing up its portfolio of cardiovascular drugs as part of its strategy to counter a possible hit to sales to its best-selling drug Keytruda from biosimilar drugs in the next few years.

Another experimental heart drug, MK-0616, helped reduce levels of low-density lipoprotein (LDL) cholesterol by between 41.2% at a low 6 mg dose and 60.9% at a higher 30 mg dose in a mid-stage study, Merck said on Monday.

Analysts have said MK-0616 would need to show a more than 50% reduction in LDL level, similar to drugs from rivals Regeneron and Sanofi SA and Amgen.

The data were presented at the American College of Cardiology's annual meeting in New Orleans.