(Reuters) - Novartis failed to convince a U.S. appeals court on Wednesday to halt MSN Pharmaceuticals' proposed generic of Novartis' blockbuster heart drug Entresto.

The U.S. Court of Appeals for the Federal Circuit upheld a Delaware federal judge's August decision that found Novartis failed to prove it was likely to win a patent lawsuit against MSN over the drug, removing a roadblock for MSN's launch of what would be the first U.S. Entresto generic.

Spokespeople and attorneys for the companies did not immediately respond to requests for comment.

Entresto is Switzerland-based Novartis' best-selling drug, bringing the company more than $6 billion in revenue last year. MSN's version of Entresto was approved by the U.S. Food and Drug Administration in July.

Novartis sued MSN and others seeking to launch Entresto generics in Delaware federal court in 2022 for allegedly infringing a patent that expires in 2026. It requested a preliminary injunction after the FDA's approval that would block MSN from launching its generic during the case, which is set to go to trial on Monday.

U.S. District Judge Richard Andrews rejected Novartis' request in August, ruling that it was not sufficiently likely to win on its infringement claims to justify the injunction. The judge paused MSN's launch of its proposed generic while Novartis appealed to the Federal Circuit.

The Washington-based appeals court affirmed Andrews' decision on Wednesday and said it saw "no clear error in the district court's analysis."

(Reporting by Blake Brittain in Washington; Editing by Richard Chang)

By Blake Brittain