There are 5 cars and 6 events for each car in the NFS Heroes Pack. You need to beat the gold medal score for all these events to unlock the achievement.
Note that the two events for each car from the Terminal Velocity pack do not need to be completed to unlock this achievement, regardless of whether or not you bought it. The Terminal Velocity events are the ones marked by a red wing icon and unlock the Jump Nitrous/Drift Tire mods.
The Jack Spots are unlocked as soon as you've purchased the pack, and are indicated by a red NFS logo. The cars in the pack are as follows:
Lamborghini Diablo SV
Nissan Skyline GT-R
Porsche 911 GT2 RS
Most Wanted BMW M3 GTR
The first four cars will be available from the start, while the BMW M3 GTR is earned by winning the Most Wanted M3 GTR event.