All Black lock Chris Jack and South African full-back Brent Russell both made debuts for the English side.
But it was a hat-trick from Richard Haughton and 25 points from number 10 Glen Jackson that helped Saracens to a huge win in Pool Four.
Jackson landed nine conversions, a penalty and a try, with Viadana's sole points coming from Calvin Howarth.
Saracens coach Alan Gaffney:
"I thought Chris Jack was outstanding. Chris is very good on the ball, good in the air and just an excellent line-out jumper.
"We've got to raise our pace, because he's so good across the ground - and we're probably not good enough at the present time to help him.
"We need to improve and make sure we get the best out of him. His fitness is fine; he hasn't played a lot of rugby lately but he just kept going."
Saracens: Brent Russell, Richard Haughton, Kevin Sorrell, Andy Farrell, Kameli Ratuvou, Glen Jackson, Neil de Kock (capt), Nick Lloyd, Fabio Ongaro, Cobus Visagie, Chris Jack, Hugh Vyvyan, Sakiusa Matadigo, Richard Hill, Ben Skirving
Replacements: Andy Kyriacou, Census Johnston, Iain Fullarton, David Seymour, Alan Dickens, Adam Powell, Edd Thrower
Viadana: Garry Law, Roberto Mariani, Samuele Pace, Matthew Harvey, Andrea Accorsi, Calvin Howarth, Steven Bortolussi, Plinio Sciamanna, Andrea Moretti (capt), Ignacio Rouyet, Cristian Bezzi, Dion Waller, Sam Harding Lance Persico, Mario Vella
Replacements: Roberto Santamaria, Jaco Erasmus, Mattia Cagna, Andrea Benatti, Corrado Pilat, Craig McGrath, Claudio Spadaro