Do threads have a distinct heap?

No. All threads share a common heap.

Each thread has a private stack, which it can quickly add and remove items from. This makes stack based memory fast, but if you use too much stack memory, as occurs in infinite recursion, you will get a stack overflow.

Since all threads share the same heap, access to the allocator/deallocator must be synchronized. There are various methods and libraries for avoiding allocator contention.

Some languages allow you to create private pools of memory, or individual heaps, which you can assign to a single thread.

By default, C has only a single heap.

That said, some allocators that are thread aware will partition the heap so that each thread has it's own area to allocate from. The idea is that this should make the heap scale better.

One example of such a heap is Hoard.

Depends on the OS. The standard c runtime on windows and unices uses a shared heap across threads. This means locking every malloc/free.

On Symbian, for example, each thread comes with its own heap, although threads can share pointers to data allocated in any heap. Symbian's design is better in my opinion since it not only eliminates the need for locking during alloc/free, but also encourages clean specification of data ownership among threads. Also in that case when a thread dies, it takes all the objects it allocated along with it - i.e. it cannot leak objects that it has allocated, which is an important property to have in mobile devices with constrained memory.

Erlang also follows a similar design where a "process" acts as a unit of garbage collection. All data is communicated between processes by copying, except for binary blobs which are reference counted (I think).