However, Sow suffered a thigh strain and was initially out for weeks, but was then ruled out until January. Having made his return in a reserve match in mid-January, Sow made his first team return, in a 3–2 defeat to Falkirk, where he set up Género Zeefuik's opener. It took until 28 February 2015 for Sow to score twice, in a 10–0 win over Cowdenbeath. Sow made twenty-two appearances, scoring eleven times and was among six Hearts players to be named in the 2014–15 Championship's Team of the Year. In the 2015–16 season, Sow started well when he scored twice, one coming from the penalty spot, in a 4–2 win over Arbroath in the Scottish League Cup first round. Sow made his Scottish Premiership debut against St Johnstone in the opening game of the season, where he had his penalty saved by Alan Mannus before Jamie Walker scored from the rebound, as Hearts won 4–3. It took until 15 August 2015, for Sow to score his first league goal of the season against Ross County, followed up with his second goal against Partick Thistle one week later. He scored again in consecutive weeks in October, against Ross County and a brace against Partick Thistle for the second time this season. Sow then added four more goals against Motherwell, Celtic, Dundee United and Motherwell again. With his contract expiring at the end of the 2015–16 season, Hearts started negotiations with Sow over a new contract. Two months after the negotiations started, the talks between the club and the player were positive, with a chance of Sow signing a new contract, but this did not stop him from attracting other clubs, such as Birmingham City, Celtic and Rangers. Former Hearts player Jimmy Sandison said it would be "football suicide if Sow left". On the last day of the transfer window, Hearts accepted a £1 million bid from an unknown Chinese club, presumed to be Henan Jianye. This led Hearts to sign Abiola Dauda on loan from Vitesse. With his move to China completed, Hearts manager Robbie Neilson left it up to Sow to decide whether or not he wanted to play in the upcoming Edinburgh Derby as it had been agreed that he could play before leaving. After leaving Hearts, Sow took to Twitter, thanking the club and wish them the best. During his time at Heart of Midlothian, Sow scored 23 times in 52 appearances in all competitions.