With medical clearance, United finalized a deal with Kamara’s previous employer, IFK Norrkoping of Sweden. D.C. did not pay a transfer fee but will compensate the Swedish team if Kamara, 22, meets performance incentives or is sold in the future.

To make room on the roster, United waived rookie midfielder Paul Clowes.

Kamara was no longer allowed to play in Sweden, where he had scored 16 goals over two seasons. U.S. and European officials have differing opinions on whether athletes with Kamara’s condition should be allowed to compete, Kasper said.

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Kamara’s acquisition comes a year after United forward Eddie Johnson was forced to retire because of a heart ailment. However, Kamara and Johnson have different conditions.

At the time of Kamara’s diagnosis Norrkoping said his condition presents “a high risk of sudden cardiac death during maximum exertion. All the experts advise against continuing football.”

Kasper said: “The player had a potential cardiac issue that could have eliminated him from playing. He was evaluated and found this not to be the case.”

The MLS consultant who cleared Kamara, Matthew Martinez of Allentown, Pa., was among the doctors who evaluated Johnson.

“There was an initial concern [about Kamara’s condition], but we went through proper medical testing and approvals from two top cardiology specialists,” Kasper said. “Certainly we went through a rigorous process, but once they cleared him to play, it gave us peace of mind.”

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Kamara will undergo testing at the end of each season, Kasper said.

The acquisition of a player with a heart history comes at a sensitive time in the soccer world. In the past week, two players have died of apparent heart attacks after collapsing during a match: Cameroon’s Patrick Ekeng, who was competing for Dinamo Bucharest in Romania, and Bernardo Ribeiro, with Friburguense in his native Brazil. Both were 26.

Kamara’s ailment was detected after Norrkoping won the Swedish championship last season, its first top-flight title in 23 years. As reward, the club qualified for the UEFA Champions League, Europe’s premier continental-wide competition. Norrkoping was to enter the tournament’s early rounds this summer. To participate, players must undergo intensive medical exams. When his heart issue was revealed, Kamara was held out of training camp.

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United took interest two months ago and, given Kamara’s medical case, “we’ve been very meticulous,” Kasper said.

The urgency to sign a forward has risen over the first two months of the MLS season. United has been shut out in four of 10 matches and scored just once in four others.

On Sunday, with Chris Rolfe suspended and Fabian Espindola sidelined for the second consecutive game with a hamstring injury, Alvaro Saborio squandered two excellent chances in the first half. United had 10 shots overall but none on target in losing, 2-0. The club will carry a 2-4-4 record into Friday’s home game against the New York Red Bulls.

United is awaiting Kamara’s international transfer certificate — MLS’s deadline is Wednesday night — and a work visa. However, because he has not played a competitive match since Nov. 8, Kamara is going to need a “preseason” of sorts, Kasper said. The club is not expecting him to contribute for quite a while.

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Kamara is not related to Columbus Crew star Kei Kamara, 31, also from Sierra Leone. Kamara is a common family name in West Africa.

“He is a player who did very well in Sweden,” Kasper said of his 5-foot-11, 161-pound acquisition. “We like his age. We like his physical characteristics. He has a nose for the goal. He’s a strong, powerful striker.”

Goal highlights: