Dublin - Defending Heineken Cup champions Leinster were drawn in the same pool as French heavyweights Clermont for the 2012/13 season on Tuesday.
The Irish province will also face Welsh region Scarlets and English club Exeter in Pool 5.
Last season's beaten finalists Ulster are in Pool 4 with Northampton, Glasgow and Castres.
Challenge Cup winners Biarritz were drawn in Pool 3 alongside English domestic league champions Harlequins, Irish minnows Connacht and Italian newcomers Zebre.
Pool 1 sees Munster line up with Edinburgh, Saracens and Racing Metro, while four-time champions Toulouse face a tough Pool 2 alongside English giants Leicester and Celtic League champions Ospreys, with Treviso making up the numbers.
Cardiff Blues and Sale will battle it out with French clubs Toulon and Montpellier for top spot in Pool 6.
Only the pool winners and the two best runners-up will progress to the knock-out phase of European club rugby's showcase tournament.
Pool 1: Munster (IRL), Edinburgh (SCO), Saracens (ENG), Racing Metro (FRA)
Pool 2: Toulouse (FRA), Leicester (ENG), Ospreys (WAL), Treviso (ITA)
Pool 3: Biarritz (FRA), Harlequins (ENG), Connacht (IRL), Zebre (ITA)
Pool 4: Northampton (ENG), Ulster (IRL), Glasgow (SCO), Castres (FRA)
Pool 5: Leinster (IRL), Clermont-Auvergne (FRA), Scarlets (WAL), Exeter (ENG)
Pool 6: Cardiff Blues (WAL), Toulon (FRA), Sale (ENG), Montpellier (FRA)
1st round: October 11-14
2nd round: October 17-20
3rd round: December 6-9
4th round: December 13-16
5th round: January 10-13, 2013
6th round: January 17-20
Quarter-finals: April 4-7
Semi-finals: April 26-28
Final: May 18 in Dublin