diff --git a/imperative/distributed/heartbeat.rkt b/imperative/distributed/heartbeat.rkt
index 86059c4..450c351 100644
--- a/imperative/distributed/heartbeat.rkt
+++ b/imperative/distributed/heartbeat.rkt
@@ -2,39 +2,49 @@
 
 (provide heartbeat)
 
+(module+ for-testing
+  (provide heartbeats-enabled?))
+
 (require "wire-protocol.rkt")
 
 (require/activate imperative-syndicate/drivers/timer)
 
 (define-logger syndicate/distributed)
 
+(define heartbeats-enabled? (make-parameter #t))
+
 ;; TODO: move heartbeats to transport level, and use separate transport-activity timeouts from
 ;; message-activity timeouts. Using message-activity only has problems when messages are large
 ;; and links are slow. Also, moving to transport level lets us use e.g. WebSocket's ping
 ;; mechanism rather than a message-level mechanism.
 (define (heartbeat who send-message teardown)
-  (define period (ping-interval))
-  (define grace (* 3 period))
+  (cond
+    [(heartbeats-enabled?)
+     (define period (ping-interval))
+     (define grace (* 3 period))
 
-  (log-syndicate/distributed-debug
-   "Peer ~v heartbeat period ~ams; must not experience silence longer than ~ams"
-   who period grace)
+     (log-syndicate/distributed-debug
+      "Peer ~v heartbeat period ~ams; must not experience silence longer than ~ams"
+      who period grace)
 
-  (field [next-ping-time 0]) ;; when we are to send the next ping
-  (field [last-received-traffic (current-inexact-milliseconds)]) ;; when we last heard from the peer
+     (field [next-ping-time 0]) ;; when we are to send the next ping
+     (field [last-received-traffic (current-inexact-milliseconds)]) ;; when we last heard from the peer
 
-  (define (schedule-next-ping!)
-    (next-ping-time (+ (current-inexact-milliseconds) period)))
+     (define (schedule-next-ping!)
+       (next-ping-time (+ (current-inexact-milliseconds) period)))
 
-  (on (asserted (later-than (next-ping-time)))
-      (schedule-next-ping!)
-      (send-message (Ping)))
+     (on (asserted (later-than (next-ping-time)))
+         (schedule-next-ping!)
+         (send-message (Ping)))
 
-  (on (asserted (later-than (+ (last-received-traffic) grace)))
-      (log-syndicate/distributed-info "Peer ~v heartbeat timeout after ~ams of inactivity"
-                                      who grace)
-      (teardown))
+     (on (asserted (later-than (+ (last-received-traffic) grace)))
+         (log-syndicate/distributed-info "Peer ~v heartbeat timeout after ~ams of inactivity"
+                                         who grace)
+         (teardown))
 
-  (lambda ()
-    (schedule-next-ping!)
-    (last-received-traffic (current-inexact-milliseconds))))
+     (lambda ()
+       (schedule-next-ping!)
+       (last-received-traffic (current-inexact-milliseconds)))]
+    [else
+     (log-syndicate/distributed-debug "Peer ~v heartbeats disabled" who)
+     void]))
diff --git a/imperative/test/distributed/nesting-confusion.rkt b/imperative/test/distributed/nesting-confusion.rkt
index 98f8f3d..9f19593 100644
--- a/imperative/test/distributed/nesting-confusion.rkt
+++ b/imperative/test/distributed/nesting-confusion.rkt
@@ -5,6 +5,9 @@
 (require imperative-syndicate/distributed)
 (require imperative-syndicate/distributed/internal-protocol)
 
+(require (submod imperative-syndicate/distributed/heartbeat for-testing))
+(heartbeats-enabled? #f)
+
 (assertion-struct researcher (name topic))
 
 (define test-address (server-loopback-connection "test"))
diff --git a/imperative/test/distributed/observation-visibility.rkt b/imperative/test/distributed/observation-visibility.rkt
index a545943..9642a69 100644
--- a/imperative/test/distributed/observation-visibility.rkt
+++ b/imperative/test/distributed/observation-visibility.rkt
@@ -5,6 +5,9 @@
 (require (only-in imperative-syndicate/lang activate))
 (require imperative-syndicate/distributed)
 
+(require (submod imperative-syndicate/distributed/heartbeat for-testing))
+(heartbeats-enabled? #f)
+
 (assertion-struct presence (who))
 
 (define test-address (server-loopback-connection "test"))