diff --git a/src/core/WakaTimeCore.ts b/src/core/WakaTimeCore.ts
index 9f7923f..0add85c 100644
--- a/src/core/WakaTimeCore.ts
+++ b/src/core/WakaTimeCore.ts
@@ -4,6 +4,11 @@ import { Tabs } from 'webextension-polyfill';
 import { AxiosUserResponse, User } from '../types/user';
 import config from '../config/config';
 import { SummariesPayload, GrandTotal } from '../types/summaries';
+import changeExtensionState from '../utils/changeExtensionState';
+import inArray from '../utils/inArray';
+import contains from '../utils/contains';
+import { SendHeartbeat } from '../types/heartbeats';
+import getDomainFromUrl from '../utils/getDomainFromUrl';
 
 class WakaTimeCore {
   tabsWithDevtoolsOpen: Tabs.Tab[];
@@ -30,6 +35,11 @@ class WakaTimeCore {
     return summariesAxiosPayload.data.data[0].grand_total;
   }
 
+  /**
+   * Checks if the user is logged in.
+   *
+   * @returns {*}
+   */
   async checkAuth(api_key = ''): Promise<User> {
     const userPayload: AxiosResponse<AxiosUserResponse> = await axios.get(
       config.currentUserApiUrl,
@@ -38,6 +48,10 @@ class WakaTimeCore {
     return userPayload.data.data;
   }
 
+  /**
+   * Depending on various factors detects the current active tab URL or domain,
+   * and sends it to WakaTime for logging.
+   */
   async recordHeartbeat(): Promise<void> {
     const items = await browser.storage.sync.get({
       blacklist: '',
@@ -45,6 +59,201 @@ class WakaTimeCore {
       loggingStyle: config.loggingStyle,
       whitelist: '',
     });
+    if (items.loggingEnabled === true) {
+      await changeExtensionState('allGood');
+
+      const newState = await browser.idle.queryState(config.detectionIntervalInSeconds);
+
+      if (newState === 'active') {
+        // Get current tab URL.
+        const tabs = await browser.tabs.query({ active: true, currentWindow: true });
+        if (tabs.length == 0) return;
+
+        const currentActiveTab = tabs[0];
+        let debug = false;
+
+        // If the current active tab has devtools open
+        if (
+          inArray(
+            currentActiveTab.id,
+            this.tabsWithDevtoolsOpen.map((tab) => tab.id),
+          )
+        ) {
+          debug = true;
+        }
+
+        if (items.loggingStyle == 'blacklist') {
+          if (!contains(currentActiveTab.url as string, items.blacklist as string)) {
+            await this.sendHeartbeat(
+              {
+                project: null,
+                url: currentActiveTab.url as string,
+              },
+              debug,
+            );
+          } else {
+            await changeExtensionState('blacklisted');
+            console.log(`${currentActiveTab.url} is on a blacklist.`);
+          }
+        }
+
+        if (items.loggingStyle == 'whitelist') {
+          const heartbeat = this.getHeartbeat(
+            currentActiveTab.url as string,
+            items.whitelist as string,
+          );
+          if (heartbeat.url) {
+            await this.sendHeartbeat(heartbeat, debug);
+          } else {
+            await changeExtensionState('whitelisted');
+            console.log(`${currentActiveTab.url} is not on a whitelist.`);
+          }
+        }
+      }
+    } else {
+      await changeExtensionState('notLogging');
+    }
+  }
+
+  /**
+   * Creates an array from list using \n as delimiter
+   * and checks if any element in list is contained in the url.
+   * Also checks if element is assigned to a project using @@ as delimiter
+   *
+   * @param url
+   * @param list
+   * @returns {object}
+   */
+  getHeartbeat(url: string, list: string) {
+    const projectIndicatorCharacters = '@@';
+
+    const lines = list.split('\n');
+    for (let i = 0; i < lines.length; i++) {
+      // strip (http:// or https://) and trailing (`/` or `@@`)
+      const cleanLine = lines[i]
+        .trim()
+        .replace(/(\/|@@)$/, '')
+        .replace(/^(?:https?:\/\/)?/i, '');
+      if (cleanLine === '') continue;
+
+      const projectIndicatorIndex = cleanLine.lastIndexOf(projectIndicatorCharacters);
+      const projectIndicatorExists = projectIndicatorIndex > -1;
+      let projectName = null;
+      let urlFromLine = cleanLine;
+      if (projectIndicatorExists) {
+        const start = projectIndicatorIndex + projectIndicatorCharacters.length;
+        projectName = cleanLine.substring(start);
+        urlFromLine = cleanLine
+          .replace(cleanLine.substring(projectIndicatorIndex), '')
+          .replace(/\/$/, '');
+      }
+      const schemaHttpExists = url.match(/^http:\/\//i);
+      const schemaHttpsExists = url.match(/^https:\/\//i);
+      let schema = '';
+      if (schemaHttpExists) {
+        schema = 'http://';
+      }
+      if (schemaHttpsExists) {
+        schema = 'https://';
+      }
+      const cleanUrl = url
+        .trim()
+        .replace(/(\/|@@)$/, '')
+        .replace(/^(?:https?:\/\/)?/i, '');
+      const startsWithUrl = cleanUrl.toLowerCase().includes(urlFromLine.toLowerCase());
+      if (startsWithUrl) {
+        return {
+          project: projectName,
+          url: schema + urlFromLine,
+        };
+      }
+    }
+
+    return {
+      project: null,
+      url: null,
+    };
+  }
+
+  /**
+   * Given the heartbeat and logging type it creates a payload and
+   * sends an ajax post request to the API.
+   *
+   * @param heartbeat
+   * @param debug
+   */
+  async sendHeartbeat(heartbeat: SendHeartbeat, debug: boolean): Promise<void> {
+    let payload = null;
+
+    const loggingType = await this.getLoggingType();
+    // Get only the domain from the entity.
+    // And send that in heartbeat
+    if (loggingType == 'domain') {
+      heartbeat.url = getDomainFromUrl(heartbeat.url);
+      payload = this.preparePayload(heartbeat, 'domain', debug);
+      console.log(payload);
+      await this.sendAjaxRequestToApi(payload);
+    }
+    // Send entity in heartbeat
+    else if (loggingType == 'url') {
+      payload = this.preparePayload(heartbeat, 'url', debug);
+      console.log(payload);
+      await this.sendAjaxRequestToApi(payload);
+    }
+  }
+
+  /**
+   * Returns a promise with logging type variable.
+   *
+   * @returns {*}
+   * @private
+   */
+  async getLoggingType(): Promise<string> {
+    const items = await browser.storage.sync.get({
+      loggingType: config.loggingType,
+    });
+
+    return items.loggingType;
+  }
+
+  /**
+   * Creates payload for the heartbeat and returns it as JSON.
+   *
+   * @param heartbeat
+   * @param type
+   * @param debug
+   * @returns {*}
+   * @private
+   */
+  preparePayload(heartbeat: SendHeartbeat, type: string, debug = false): Record<string, unknown> {
+    return {
+      entity: heartbeat.url,
+      is_debugging: debug,
+      plugin: 'browser-wakatime/' + config.version,
+      project: heartbeat.project ?? '<<LAST_PROJECT>>',
+      time: moment().format('X'),
+      type: type,
+    };
+  }
+
+  /**
+   * Sends AJAX request with payload to the heartbeat API as JSON.
+   *
+   * @param payload
+   * @param method
+   * @returns {*}
+   */
+  async sendAjaxRequestToApi(payload: Record<string, unknown>, api_key = '') {
+    try {
+      const response = await axios.post(config.heartbeatApiUrl, payload, {
+        params: {
+          api_key,
+        },
+      });
+      return response.data;
+    } catch (err: unknown) {
+      await changeExtensionState('notSignedIn');
+    }
   }
 }
 
diff --git a/src/types/heartbeats.ts b/src/types/heartbeats.ts
index e178266..8067433 100644
--- a/src/types/heartbeats.ts
+++ b/src/types/heartbeats.ts
@@ -26,3 +26,8 @@ export interface Datum {
   user_agent_id: string;
   user_id: string;
 }
+
+export interface SendHeartbeat {
+  project: string | null;
+  url: string;
+}
diff --git a/src/utils/inArray.ts b/src/utils/inArray.ts
index d9d914c..55696eb 100644
--- a/src/utils/inArray.ts
+++ b/src/utils/inArray.ts
@@ -1,7 +1,7 @@
 /**
  * Returns boolean if needle is found in haystack or not.
  */
-export default function in_array<T>(needle: T, haystack: T[]): boolean {
+export default function inArray<T>(needle: T, haystack: T[]): boolean {
   for (let i = 0; i < haystack.length; i++) {
     if (needle == haystack[i]) {
       return true;