radare2's dm subcommands can also display a map of the heap which is useful for those who are interested in inspecting the heap and its content. Simply execute dmh to show a map of the heap:

[0x7fae46236ca6]> dmh
  Malloc chunk @ 0x55a7ecbce250 [size: 0x411][allocated]
  Top chunk @ 0x55a7ecbce660 - [brk_start: 0x55a7ecbce000, brk_end: 0x55a7ecbef000]

You can also see a graph layout of the heap:

[0x7fae46236ca6]> dmhg
Heap Layout
    |    Malloc chunk @ 0x55a7ecbce000   |
    | size: 0x251                        |
    |  fd: 0x0, bk: 0x0                  |
  |    Malloc chunk @ 0x55a7ecbce250            |
  | size: 0x411                                 |
  |  fd: 0x57202c6f6c6c6548, bk: 0xa21646c726f  |
|  Top chunk @ 0x55a7ecbce660                        |
| [brk_start:0x55a7ecbce000, brk_end:0x55a7ecbef000] |

Another heap commands can be found under dmh, check dmh? for the full list.

[0x00000000]> dmh?
|Usage:  dmh # Memory map heap
| dmh                 List chunks in heap segment
| dmh [malloc_state]  List heap chunks of a particular arena
| dmha                List all malloc_state instances in application
| dmhb                Display all parsed Double linked list of main_arena's bins instance
| dmhb [bin_num|bin_num:malloc_state]          Display parsed double linked list of bins instance from a particular arena
| dmhbg [bin_num]     Display double linked list graph of main_arena's bin [Under developemnt]
| dmhc @[chunk_addr]  Display malloc_chunk struct for a given malloc chunk
| dmhf                Display all parsed fastbins of main_arena's fastbinY instance
| dmhf [fastbin_num|fastbin_num:malloc_state]  Display parsed single linked list in fastbinY instance from a particular arena
| dmhg                Display heap graph of heap segment
| dmhg [malloc_state] Display heap graph of a particular arena
| dmhi @[malloc_state]Display heap_info structure/structures for a given arena
| dmhm                List all elements of struct malloc_state of main thread (main_arena)
| dmhm [malloc_state] List all malloc_state instance of a particular arena
| dmht                Display all parsed thead cache bins of main_arena's tcache instance
| dmh?                Show map heap help

To print safe-linked lists (glibc >= 2.32) with demangled pointers, the variable dbg.glibc.demangle must be true.