Heliovaara and Patten recently moved to number one in the world in the ATP Doubles ranking despite losing the French Open Final a fortnight ago, and again they have fallen short in a Final, going down to the duo from El Salvador and Croatia.
It puts a dent in what had been a perfect start to their grass court season, winning their First Round match in straight sets before needing two three-set victories to reach the showpiece match of the London tournament.
The pair will seek to improve before they attempt to regain the Wimbledon title they won together in 2024, the first of two Grand Slam titles they have won as a partnership.
A loss of serve in the opening game set the tone for the match, before another break by Arevalo and Pavic in game five but the number four seeds 4-1 ahead, before they kept control of the first set, taking it 6-2 with their maiden set point.
Heliovaara and Patten held off a break point in game three as they came out stronger in set two, but finally they were broken in game nine, before career Grand Slam winner Pavic and two-time French Open winner Arevalo secured the set 6-4 with minimal fuss in the next game.
Both pairs now turn their focus to Wimbledon, where the Men's Doubles is scheduled to begin on 1st July.