It is completely fine to make a takeout double with a 3 card major. The double says that we have points, and 3-4 of each major typically. Partner can easily have 5+ hearts.
The most important signals
Double or bid?
Bid as high as possible!
Defending against a multi 2♦
Transfer or not?
Nv compete
How strong vulnerable?
Preempt suit quality
6322 and 7222
2♣ opening
Doubleton lead
Passive lead
When to lead active
1N with 5422
Negative double
Takeout double
Splinters
Competing partscore
Try not double
Ace Ace King
2 level overcall