EDITOR'S NOTE: This story has been updated to clarify the difference between the experimental compound and the studies of its effects.

An injectable heart drug licensed to Amgen Inc. failed to perform as expected in a clinical study, but the company plans to await further test results before deciding whether to continue or abandon development of the drug.

The Thousand Oaks pharmaceutical company holds an exclusive worldwide license to commercialize omecamtiv mecarbil, a compound developed by Cytokinetics Inc., a South San Francisco medical research company. The two companies conducted a study called ATOMIC-AHF to see if the drug could help patients keep breathing after their heart stops.

However, in a study of 613 patients hospitalized for acute heart failure, the injections failed to prevent shortness of breath to the degree researchers expected. The results were announced Tuesday at the ESC Congress 2013, a medical conference in Amsterdam.

The companies are conducting a second study, called COSMIC-HF, to see if an oral version of the medication will help heart patients.

“Although ATOMIC-AHF did not achieve its primary efficacy endpoint, we are encouraged by the data from this study,” Dr. Sean Harper, executive vice president of research and development at Amgen, said in a statement. “We look forward to the data from the COSMIC-HF study, which together with the data from ATOMIC-AHF will inform our decision on whether to progress omecamtiv mecarbil into Phase 3 clinical trials.”

Shares of Amgen closed up $2.07 or 2 percent at $111.01 on the Nasdaq.