diff --git a/simulate-nis2.php b/simulate-nis2.php
index 83bf325..00282f6 100644
--- a/simulate-nis2.php
+++ b/simulate-nis2.php
@@ -85,6 +85,7 @@ $S = [
 
 function simLog(string $msg, string $type = 'info'): void
 {
+    static $lastHeartbeat = 0;
     $ts = date('H:i:s');
     if (IS_CLI) {
         $prefix = [
@@ -99,6 +100,12 @@ function simLog(string $msg, string $type = 'info'): void
         echo "[$ts] {$prefix} {$msg}\n";
         flush();
     } else {
+        // Heartbeat SSE ogni 25s — mantiene viva la connessione attraverso proxy (pattern lg231)
+        $now = time();
+        if ($now - $lastHeartbeat >= 25) {
+            echo ": heartbeat " . $ts . "\n\n";
+            $lastHeartbeat = $now;
+        }
         echo 'data: ' . json_encode(['t' => $type, 'm' => "[$ts] $msg"]) . "\n\n";
         flush();
     }