The 24-year-old, who was born in the United States, holds dual American and Norwegian citizenship and began his career in Norway with Valerenga.
Since then the towering 6ft5in striker has played in Spain and Portugal before joining Bulgarian club Litex Lovech.
However, after signing a three-year deal to raise spirits at Tynecastle after Thursday’s shock Europa League defeat by Maltese outfit Birkirkara, Johnsen insists he knows plenty about Scottish football.
He said: “I want to be able to help out, with assists and not just goals, to help the team to win games and try to get up to the top of the league and push for it.
“This league is looking pretty tough right now. I know about Rangers, they’re just coming back, but it’s time for Hearts. We have high expectations and I want to fulfil those.
“After I knew I was going to sign for Hearts I did my research, getting to know the team, the players, the coach, how they play, who they’re playing and which teams are better than others.
“But since I was about 14 I’ve been watching Scottish football. We always watched when Rangers were playing Celtic.
“The problem is Europe is changing, people want to go down south to Turkey and all these places.
“People have to know that the real football is here, the real history is here and I want to be here.”
Johnsen, born in North Carolina to a Norwegian father and American mother, is confident he will be able to make an impact. He added: “It’s a little bit crazy to be here but I’m just worried now about getting on the field, getting to know the guys and starting to play.
“I felt wanted, so I wanted to come here, somewhere I could start afresh and understand that the people want you to be there – family.
“At first, I went to Norway at 18 to Valerenga and played with some big players, who now play in the Bundesliga and other places.
“I bounced around after that and went to Spain and to Portugal and then an offer came to go to Bulgaria, which was a new step for me, playing Europa League and playing in the first division against some big clubs.
“That was a good step for me, to learn, and now I’m ready to come to Hearts.”
The recruitment of Johnsen and former Celtic striker Tony Watt, who arrived on loan from Charlton this week will put immediate pressure on Juanma and Conor Sammon, who is in possession of the main striker’s jersey, and who scored his first goal in four competitive outings for the club, in Thursday’s defeat.
The former Kilmarnock, Wigan and Derby County frontman has yet to win over the Tynecastle fans, and his name was read out as a man-of-the-match during the final moments of that defeat, the announcement was greeted with a hail of boos.
Sammon, however, insists he will take no notice, focusing instead on moving on from the disappointment.
“I wasn’t aware of that, didn’t hear any of that,” he said of the personal reaction.
“It doesn’t interest me at all, Man of the Match or whatever. I’m fully aware if I’ve had a good game or if there are aspects I can improve on. Personally, I’m my own worst critic. So I don’t really take much notice from anything that goes on outside.”
On the fans, who also booed the team’s performance at the end of the 90 minutes, he added: “It’s up to us to turn them around. Absolutely. The support here is incredible. At the start of the game, there was an amazing atmosphere. As a player, going out to play in front of that, it’s just so powerful.
“We will look to kick on [from the defeat], try to get some positives from it – and learn from the negative experience.”