There's already a Slack integration with Heartbeat using Zapier :) You can select the triggers you want from Heartbeat, then configure the message you want in Slack. You can choose if it goes to a channel, or is a direct message.

Here's the official page on it: https://zapier.com/apps/heartbeat/integrations/slack

I did a post about this in Heartbeat's user community, The Hearth, and you can ask about it in the Automations channel if you have questions.

It's highly configurable, and really helpful. You can automate Heartbeat to Slack, and vice a versa. :)