The Heartbeat trigger only works if a device is "Offline" and comes "Online".
PDQ sends all 5 min a ping to your devices to check the offline/online status.
Heartbeat doesen't mean you kick off a "heartbeat" via Ctrl+H inside PDQ Inventory.
Because a heartbeat via Ctrl+H is only a ping and doesen't change the status from offline to online if the device is already online.
Even rebooting a device doesen't help, because if the reboot happens between the ping window, PDQ doesen't notice the short offline time.
If you want a deployment now, click with the right mousebutton on the deployment schedule -> start schedule -> Current Package.....