Novartis AG (NVS - Get Report)  shares fell Wednesday after it said a potentially key cardiovascular treatment had failed a global clinical trial, putting doubt over the group's ability to offset slowing heart disease drug sales.

Serelaxin, a drug that treats patients with acute heart failure, was rejected by both the U.S. Food & Drug Administration and European regulators in 2014, both of which asked for further evidence of its ability to prevent heart disease from worsening as part of a treatment program.

"We are disappointed this study did not confirm the efficacy of RLX030 in acute heart failure, especially given the urgent need for effective new treatments for this condition," said chief medical officer Vas Narasimhan. "We will continue to further analyze the data to better understand and learn from these results as well as evaluate next steps for the overall program. We remain committed to improving and extending the lives of patients with cardiovascular disease and will continue to invest in ways to improve their outcomes."

The failure could pressure the company to address the slowdown in sales of its cardiovascular drug Diovan which accounted for $1.07 billion in 2016 sales, down from $1.28 billion in 2015. Diovan lost its EU exclusivity in 2011 and its U.S. exclusivity in 2012. 

Novartis shares were marked 1.24% lower at Srf73.43 near the close of trading Wednesday against a broader 0.48% decline for the SMI benchmark. The shares have fallen more than 1% over the past three months compared to a 4.6% advance for the Stoxx Europe TMI Pharmaceuticals index.