The 30-year-old has agreed personal terms with the English Premiership club and was undergoing a medical on Friday.

A fee of �2m has been agreed, Hearts having rejected an initial offer of �1.5m.

Hearts chief executive Chris Robinson says he is "very sorry" to see Niemi leave but is "happy" with the deal.

It is believed that it involves a sell-on clause should the goalkeeper leave St Mary's.

Southampton had hoped that Niemi would make his debut against Liverpool on Saturday, but he is instead in the Hearts squad to face Dunfermline Athletic.

Chairman Rupert Lowe said: "We hope the deal will go through quite smoothly, because everything seems to be settled and we are delighted to have got him.

"He is the first choice for Finland and keeps Peter Enckelman and Jussi Jaaskelainen out of the national team.

"He speaks perfect English, organises the defence well and we hope he will make a major contribution.

"He's the perfect age for a keeper and fans will no doubt recall that he played a blinder for Finland to keep out Germany so England qualified for the World Cup."

Saints boss Gordon Strachan tried to sign Niemi from FC Copenhagen when was manager of Coventry City, but the Finn chose Rangers instead.

Niemi found first-team opportunities hard to come by at Ibrox and moved to Hearts.

But financial problems meant the Edinburgh side had to sell their star performer.

Niemi's imminent arrival at Southampton is likely to mean bad news for long-time first-choice Paul Jones, who made an error for Wales in the 1-1 draw with Croatia on Wednesday.