Can you exhaust Kai'Sa to float 1 power and then immediately exhaust Heimerdinger to float a second power?

Ruling: Yes, you can exhaust Kai'Sa to float 1 power and then immediately exhaust Heimerdinger to float a second power in both open and closed game states.

Sequence: Open state (during your turn with priority):

• Activate Kai'Sa's effect
• Effect resolves and you float 1 power
• You still have priority, so activate Heimerdinger's effect
• Float another 1 power

Closed state (reacting to opponent):

• Opponent activates an ability A and passes priority
• You react with Kai'Sa's effect (cannot be reacted to)
• Kai'Sa's effect resolves and you float 1 power
• Priority returns to opponent for effect A
• If opponent passes priority, you can chain Heimerdinger's effect
• Heimerdinger's effect resolves and you float another 1 power