I'm glad you have a working solution using one of the async libs, because that's the way it should be done. However, here's a semi-tested version using just IO::Socket and IO::Select as an example of one way it could have been done.

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11122630
use warnings;
use IO::Socket;
use IO::Select;

my $port = 5000;
my $hello = "Hello <VERSION>\n";
my $interval = 10;
my $heartbeat = "HeartBeat\n";

my $listen = IO::Socket::INET->new(
  LocalPort => $port,
  Listen => 10,
  Reuse => 1,
  ) or die $@;
my $sel = IO::Select->new($listen);
my %clients;

while( 1 )
  {
  for my $fh ( $sel->can_read(1) )
    {
    if( $fh == $listen )
      {
      my $client = $listen->accept;
      $clients{$client} = { client => $client, heartbeat => time + $in
+terval };
      $sel->add( $client );
      print $client $hello;
      }
    elsif( sysread $fh, my $buf, 4096 )
      {
      print "got: $buf";
      }
    else
      {
      $sel->remove( $fh );
      delete $clients{ $fh };
      }
    }
  for my $ref ( values %clients )
    {
    if( time >= $ref->{heartbeat} )
      {
      print { $ref->{client} } $heartbeat;
      $ref->{heartbeat} = time + $interval;
      }
    }
  }
[download]

I tested it with multiple telnets as clients and it happily heartbeats away, even with clients coming and going...