diff --git a/CHANGELOG.md b/CHANGELOG.md
index 90a60ddd8..a366e9828 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,7 @@
 
 ### Fixes
 - Heartbeat replies now strip repeated `HEARTBEAT_OK` tails to avoid accidental “OK OK” spam.
+- Heartbeat failure logs now include the error reason instead of `[object Object]`.
 - Duration strings now accept `h` (hours) where durations are parsed (e.g., heartbeat intervals).
 - WhatsApp send now preserves existing JIDs (including group `@g.us`) instead of coercing to `@s.whatsapp.net`. (Thanks @arun-8687.)
 - Telegram/WhatsApp: reply context stays in `Body`/`ReplyTo*`, but outbound replies no longer thread to the original message. (Thanks @joshp123 for the PR and follow-up question.)
diff --git a/src/infra/heartbeat-runner.ts b/src/infra/heartbeat-runner.ts
index 53b7f3f6e..dc0045c1d 100644
--- a/src/infra/heartbeat-runner.ts
+++ b/src/infra/heartbeat-runner.ts
@@ -11,6 +11,7 @@ import {
   saveSessionStore,
   type SessionEntry,
 } from "../config/sessions.js";
+import { formatErrorMessage } from "../infra/errors.js";
 import { createSubsystemLogger } from "../logging.js";
 import { getQueueSize } from "../process/command-queue.js";
 import { defaultRuntime, type RuntimeEnv } from "../runtime.js";
@@ -367,13 +368,14 @@ export async function runHeartbeatOnce(opts: {
     });
     return { status: "ran", durationMs: Date.now() - startedAt };
   } catch (err) {
+    const reason = formatErrorMessage(err);
     emitHeartbeatEvent({
       status: "failed",
-      reason: String(err),
+      reason,
       durationMs: Date.now() - startedAt,
     });
-    log.error("heartbeat failed", { error: String(err) });
-    return { status: "failed", reason: String(err) };
+    log.error(`heartbeat failed: ${reason}`, { error: reason });
+    return { status: "failed", reason };
   }
 }