diff --git a/packages/tracing/src/idletransaction.ts b/packages/tracing/src/idletransaction.ts
index c30f8170769c..81319bcc91e0 100644
--- a/packages/tracing/src/idletransaction.ts
+++ b/packages/tracing/src/idletransaction.ts
@@ -7,6 +7,7 @@ import { SpanStatus } from './spanstatus';
 import { Transaction } from './transaction';
 
 export const DEFAULT_IDLE_TIMEOUT = 1000;
+export const HEARTBEAT_INTERVAL = 5000;
 
 /**
  * @inheritDoc
@@ -55,9 +56,6 @@ export class IdleTransaction extends Transaction {
   // Activities store a list of active spans
   public activities: Record<string, boolean> = {};
 
-  // Stores reference to the timeout that calls _beat().
-  private _heartbeatTimer: number = 0;
-
   // Track state of activities in previous heartbeat
   private _prevHeartbeatString: string | undefined;
 
@@ -69,15 +67,19 @@ export class IdleTransaction extends Transaction {
 
   private readonly _beforeFinishCallbacks: BeforeFinishCallback[] = [];
 
-  // If a transaction is created and no activities are added, we want to make sure that
-  // it times out properly. This is cleared and not used when activities are added.
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  private _initTimeout: any;
+  /**
+   * If a transaction is created and no activities are added, we want to make sure that
+   * it times out properly. This is cleared and not used when activities are added.
+   */
+  private _initTimeout: ReturnType<typeof setTimeout> | undefined;
 
   public constructor(
     transactionContext: TransactionContext,
     private readonly _idleHub?: Hub,
-    // The time to wait in ms until the idle transaction will be finished. Default: 1000
+    /**
+     * The time to wait in ms until the idle transaction will be finished.
+     * @default 1000
+     */
     private readonly _idleTimeout: number = DEFAULT_IDLE_TIMEOUT,
     // If an idle transaction should be put itself on and off the scope automatically.
     private readonly _onScope: boolean = false,
@@ -232,14 +234,12 @@ export class IdleTransaction extends Transaction {
    * If this occurs we finish the transaction.
    */
   private _beat(): void {
-    clearTimeout(this._heartbeatTimer);
     // We should not be running heartbeat if the idle transaction is finished.
     if (this._finished) {
       return;
     }
 
-    const keys = Object.keys(this.activities);
-    const heartbeatString = keys.length ? keys.reduce((prev: string, current: string) => prev + current) : '';
+    const heartbeatString = Object.keys(this.activities).join('');
 
     if (heartbeatString === this._prevHeartbeatString) {
       this._heartbeatCounter += 1;
@@ -264,9 +264,9 @@ export class IdleTransaction extends Transaction {
    */
   private _pingHeartbeat(): void {
     logger.log(`pinging Heartbeat -> current counter: ${this._heartbeatCounter}`);
-    this._heartbeatTimer = (setTimeout(() => {
+    setTimeout(() => {
       this._beat();
-    }, 5000) as unknown) as number;
+    }, HEARTBEAT_INTERVAL);
   }
 }
 
diff --git a/packages/tracing/test/idletransaction.test.ts b/packages/tracing/test/idletransaction.test.ts
index d9a4f4cbe791..f6d5323b5f53 100644
--- a/packages/tracing/test/idletransaction.test.ts
+++ b/packages/tracing/test/idletransaction.test.ts
@@ -1,7 +1,12 @@
 import { BrowserClient } from '@sentry/browser';
 import { Hub } from '@sentry/hub';
 
-import { DEFAULT_IDLE_TIMEOUT, IdleTransaction, IdleTransactionSpanRecorder } from '../src/idletransaction';
+import {
+  DEFAULT_IDLE_TIMEOUT,
+  HEARTBEAT_INTERVAL,
+  IdleTransaction,
+  IdleTransactionSpanRecorder,
+} from '../src/idletransaction';
 import { Span } from '../src/span';
 import { SpanStatus } from '../src/spanstatus';
 
@@ -13,7 +18,7 @@ beforeEach(() => {
 describe('IdleTransaction', () => {
   describe('onScope', () => {
     it('sets the transaction on the scope on creation if onScope is true', () => {
-      const transaction = new IdleTransaction({ name: 'foo' }, hub, 1000, true);
+      const transaction = new IdleTransaction({ name: 'foo' }, hub, DEFAULT_IDLE_TIMEOUT, true);
       transaction.initSpanRecorder(10);
 
       hub.configureScope(s => {
@@ -22,7 +27,7 @@ describe('IdleTransaction', () => {
     });
 
     it('does not set the transaction on the scope on creation if onScope is falsey', () => {
-      const transaction = new IdleTransaction({ name: 'foo' }, hub, 1000);
+      const transaction = new IdleTransaction({ name: 'foo' }, hub, DEFAULT_IDLE_TIMEOUT);
       transaction.initSpanRecorder(10);
 
       hub.configureScope(s => {
@@ -31,7 +36,7 @@ describe('IdleTransaction', () => {
     });
 
     it('removes sampled transaction from scope on finish if onScope is true', () => {
-      const transaction = new IdleTransaction({ name: 'foo' }, hub, 1000, true);
+      const transaction = new IdleTransaction({ name: 'foo' }, hub, DEFAULT_IDLE_TIMEOUT, true);
       transaction.initSpanRecorder(10);
 
       transaction.finish();
@@ -43,7 +48,7 @@ describe('IdleTransaction', () => {
     });
 
     it('removes unsampled transaction from scope on finish if onScope is true', () => {
-      const transaction = new IdleTransaction({ name: 'foo', sampled: false }, hub, 1000, true);
+      const transaction = new IdleTransaction({ name: 'foo', sampled: false }, hub, DEFAULT_IDLE_TIMEOUT, true);
 
       transaction.finish();
       jest.runAllTimers();
@@ -59,7 +64,7 @@ describe('IdleTransaction', () => {
   });
 
   it('push and pops activities', () => {
-    const transaction = new IdleTransaction({ name: 'foo' }, hub, 1000);
+    const transaction = new IdleTransaction({ name: 'foo' }, hub, DEFAULT_IDLE_TIMEOUT);
     const mockFinish = jest.spyOn(transaction, 'finish');
     transaction.initSpanRecorder(10);
     expect(transaction.activities).toMatchObject({});
@@ -77,7 +82,7 @@ describe('IdleTransaction', () => {
   });
 
   it('does not push activities if a span already has an end timestamp', () => {
-    const transaction = new IdleTransaction({ name: 'foo' }, hub, 1000);
+    const transaction = new IdleTransaction({ name: 'foo' }, hub, DEFAULT_IDLE_TIMEOUT);
     transaction.initSpanRecorder(10);
     expect(transaction.activities).toMatchObject({});
 
@@ -86,7 +91,7 @@ describe('IdleTransaction', () => {
   });
 
   it('does not finish if there are still active activities', () => {
-    const transaction = new IdleTransaction({ name: 'foo' }, hub, 1000);
+    const transaction = new IdleTransaction({ name: 'foo' }, hub, DEFAULT_IDLE_TIMEOUT);
     const mockFinish = jest.spyOn(transaction, 'finish');
     transaction.initSpanRecorder(10);
     expect(transaction.activities).toMatchObject({});
@@ -105,7 +110,7 @@ describe('IdleTransaction', () => {
   it('calls beforeFinish callback before finishing', () => {
     const mockCallback1 = jest.fn();
     const mockCallback2 = jest.fn();
-    const transaction = new IdleTransaction({ name: 'foo' }, hub, 1000);
+    const transaction = new IdleTransaction({ name: 'foo' }, hub, DEFAULT_IDLE_TIMEOUT);
     transaction.initSpanRecorder(10);
     transaction.registerBeforeFinishCallback(mockCallback1);
     transaction.registerBeforeFinishCallback(mockCallback2);
@@ -124,7 +129,7 @@ describe('IdleTransaction', () => {
   });
 
   it('filters spans on finish', () => {
-    const transaction = new IdleTransaction({ name: 'foo', startTimestamp: 1234 }, hub, 1000);
+    const transaction = new IdleTransaction({ name: 'foo', startTimestamp: 1234 }, hub, DEFAULT_IDLE_TIMEOUT);
     transaction.initSpanRecorder(10);
 
     // regular child - should be kept
@@ -158,7 +163,7 @@ describe('IdleTransaction', () => {
 
   describe('_initTimeout', () => {
     it('finishes if no activities are added to the transaction', () => {
-      const transaction = new IdleTransaction({ name: 'foo', startTimestamp: 1234 }, hub, 1000);
+      const transaction = new IdleTransaction({ name: 'foo', startTimestamp: 1234 }, hub, DEFAULT_IDLE_TIMEOUT);
       transaction.initSpanRecorder(10);
 
       jest.advanceTimersByTime(DEFAULT_IDLE_TIMEOUT);
@@ -166,7 +171,7 @@ describe('IdleTransaction', () => {
     });
 
     it('does not finish if a activity is started', () => {
-      const transaction = new IdleTransaction({ name: 'foo', startTimestamp: 1234 }, hub, 1000);
+      const transaction = new IdleTransaction({ name: 'foo', startTimestamp: 1234 }, hub, DEFAULT_IDLE_TIMEOUT);
       transaction.initSpanRecorder(10);
       transaction.startChild({});
 
@@ -177,7 +182,6 @@ describe('IdleTransaction', () => {
 
   describe('heartbeat', () => {
     it('does not mark transaction as `DeadlineExceeded` if idle timeout has not been reached', () => {
-      const HEARTBEAT_INTERVAL = 5000;
       // 20s to exceed 3 heartbeats
       const transaction = new IdleTransaction({ name: 'foo' }, hub, 20000);
       const mockFinish = jest.spyOn(transaction, 'finish');
@@ -202,7 +206,7 @@ describe('IdleTransaction', () => {
     });
 
     it('finishes a transaction after 3 beats', () => {
-      const transaction = new IdleTransaction({ name: 'foo' }, hub, 1000);
+      const transaction = new IdleTransaction({ name: 'foo' }, hub, DEFAULT_IDLE_TIMEOUT);
       const mockFinish = jest.spyOn(transaction, 'finish');
       transaction.initSpanRecorder(10);
 
@@ -223,7 +227,7 @@ describe('IdleTransaction', () => {
     });
 
     it('resets after new activities are added', () => {
-      const transaction = new IdleTransaction({ name: 'foo' }, hub, 1000);
+      const transaction = new IdleTransaction({ name: 'foo' }, hub, DEFAULT_IDLE_TIMEOUT);
       const mockFinish = jest.spyOn(transaction, 'finish');
       transaction.initSpanRecorder(10);
 
@@ -315,7 +319,7 @@ describe('IdleTransactionSpanRecorder', () => {
     const mockPushActivity = jest.fn();
     const mockPopActivity = jest.fn();
 
-    const transaction = new IdleTransaction({ name: 'foo' }, hub, 1000);
+    const transaction = new IdleTransaction({ name: 'foo' }, hub, DEFAULT_IDLE_TIMEOUT);
     const spanRecorder = new IdleTransactionSpanRecorder(mockPushActivity, mockPopActivity, transaction.spanId, 10);
 
     spanRecorder.add(transaction);