diff --git a/firmware/app/zedmon/ina.c b/firmware/app/zedmon/ina.c
index 2bb3238..4ad7485 100644
--- a/firmware/app/zedmon/ina.c
+++ b/firmware/app/zedmon/ina.c
@@ -4,6 +4,7 @@
 #include <assert.h>
 #include <err.h>
 #include <dev/i2c.h>
+#include <kernel/timer.h>
 #include <lib/cbuf.h>
 #include <lib/console.h>
 #include <platform.h>
@@ -16,10 +17,18 @@
 
 typedef struct __attribute__((packed)) {
     lk_bigtime_t time;
-    uint8_t channel;
+    uint8_t type:2;
+    uint8_t channel:6;
 } ina_alert_event_t;
 
+
+enum event_type {
+    EVENT_TYPE_SAMPLE = 0x0,
+    EVENT_TYPE_HEARTBEAT = 0x1,
+};
+
 static cbuf_t ina_alert_events;
+static timer_t ina_heartbeat_timer;
 
 static bool (*ina_sample)(uint16_t *v_shunt, uint16_t *v_bus);
 static bool ina_initialized = false;
@@ -28,7 +37,17 @@
 static uint32_t ina_samples;
 static uint16_t ina_v_shunt;
 static uint16_t ina_v_bus;
+static uint16_t ina_samples_since_heartbeat;
 
+// This exepects to be called from irq context.
+bool send_irq_event(ina_alert_event_t *event) {
+    // This won't race because we're in irq context.
+    if (cbuf_space_avail(&ina_alert_events) >= sizeof(*event)) {
+        cbuf_write(&ina_alert_events, event, sizeof(*event), false);
+        return true;
+    }
+    return false;
+}
 
 bool ina_alert_irq(int index, uint64_t timestamp) {
     // We only handle a single channel right now.
@@ -39,16 +58,22 @@
     }
 
     ina_alert_event_t event = {
+        .type = EVENT_TYPE_SAMPLE,
         .channel = 0,
         .time = timestamp,
     };
 
-    // This won't race because we're in interrupt context.
-    if (cbuf_space_avail(&ina_alert_events) >= sizeof(event)) {
-        cbuf_write(&ina_alert_events, &event, sizeof(event), false);
-        return true;
-    }
-    return false;
+    return send_irq_event(&event);
+}
+
+enum handler_return ina_heartbeat_handler(struct timer *timer, lk_time_t now, void *arg){
+    ina_alert_event_t event = {
+        .type = EVENT_TYPE_HEARTBEAT,
+        .channel = 0,
+        .time = 0,
+    };
+
+    return send_irq_event(&event);
 }
 
 void ina_init(void) {
@@ -62,12 +87,15 @@
         ina_sample = ina231_sample;
     }
 
+    timer_initialize(&ina_heartbeat_timer);
     ina_initialized = true;
 
     // call sample once to unstick the conversion ready flag.
     uint16_t v_shunt;
     uint16_t v_bus;
     ina_sample(&v_shunt, &v_bus);
+
+    timer_set_periodic(&ina_heartbeat_timer, 1000, ina_heartbeat_handler, NULL);
 }
 
 
@@ -83,15 +111,32 @@
         uint16_t v_shunt;
         uint16_t v_bus;
 
+        // If we miss an alert signal edge, we'll stop sampling.  To protect
+        // against this, we do an extra sample if we've gotten no samples
+        // between two heartbeats.
+        if (event.type == EVENT_TYPE_HEARTBEAT) {
+            uint16_t samples = ina_samples_since_heartbeat;
+            ina_samples_since_heartbeat = 0;
+            if (samples > 0) {
+                continue;
+            }
+            // Kick off a read below to restart the pipeline.
+        }
+
+
         if (!ina_sample(&v_shunt, &v_bus)) {
             ina_errors++;
             continue;
         }
 
-        ina_v_shunt = v_shunt;
-        ina_v_bus = v_bus;
-        ina_samples++;
-        zedmon_usb_add_sample(event.time, v_shunt, v_bus);
+        // Don't report heartbeat samples.
+        if (event.type == EVENT_TYPE_SAMPLE) {
+            ina_v_shunt = v_shunt;
+            ina_v_bus = v_bus;
+            ina_samples++;
+            ina_samples_since_heartbeat++;
+            zedmon_usb_add_sample(event.time, v_shunt, v_bus);
+        }
     }
 }