diff --git a/ui/src/pages/AgentHealth/AgentHealth.tsx b/ui/src/pages/AgentHealth/AgentHealth.tsx
index c7bcfcbe..0087b644 100644
--- a/ui/src/pages/AgentHealth/AgentHealth.tsx
+++ b/ui/src/pages/AgentHealth/AgentHealth.tsx
@@ -80,6 +80,16 @@ function appHealth(group: AppGroup): 'success' | 'warning' | 'error' {
   return 'success';
 }
 
+function latestHeartbeat(group: AppGroup): string | undefined {
+  let latest: string | undefined;
+  for (const inst of group.instances) {
+    if (inst.lastHeartbeat && (!latest || inst.lastHeartbeat > latest)) {
+      latest = inst.lastHeartbeat;
+    }
+  }
+  return latest;
+}
+
 // ── Detail sub-components ────────────────────────────────────────────────────
 
 const LOG_LEVEL_ITEMS: ButtonGroupItem[] = [
@@ -96,6 +106,40 @@ const LOG_SOURCE_ITEMS: ButtonGroupItem[] = [
   { value: 'container', label: 'Container' },
 ];
 
+function CompactAppCard({ group, onExpand }: { group: AppGroup; onExpand: () => void }) {
+  const health = appHealth(group);
+  const heartbeat = latestHeartbeat(group);
+  const isHealthy = health === 'success';
+
+  const variantClass =
+    health === 'success' ? styles.compactCardSuccess
+    : health === 'warning' ? styles.compactCardWarning
+    : styles.compactCardError;
+
+  return (
+    <div
+      className={`${styles.compactCard} ${variantClass}`}
+      onClick={onExpand}
+      role="button"
+      tabIndex={0}
+      onKeyDown={(e) => { if (e.key === 'Enter' || e.key === ' ') onExpand(); }}
+    >
+      <div className={styles.compactCardHeader}>
+        <span className={styles.compactCardName}>{group.appId}</span>
+        <ChevronRight size={14} className={styles.compactCardChevron} />
+      </div>
+      <div className={styles.compactCardMeta}>
+        <span className={styles.compactCardLive}>
+          {group.liveCount}/{group.instances.length} live
+        </span>
+        <span className={isHealthy ? styles.compactCardHeartbeat : styles.compactCardHeartbeatWarn}>
+          {heartbeat ? timeAgo(heartbeat) : '\u2014'}
+        </span>
+      </div>
+    </div>
+  );
+}
+
 // ── AgentHealth page ─────────────────────────────────────────────────────────
 
 export default function AgentHealth() {
@@ -550,60 +594,135 @@ export default function AgentHealth() {
 
 
       {/* Group cards grid */}
-      <div className={isFullWidth ? styles.groupGridSingle : styles.groupGrid}>
-        {groups.map((group) => (
-          <GroupCard
-            key={group.appId}
-            title={group.appId}
-            accent={appHealth(group)}
-            headerRight={
-              <Badge
-                label={`${group.liveCount}/${group.instances.length} LIVE`}
-                color={appHealth(group)}
-                variant="filled"
-              />
-            }
-            meta={
-              <div className={styles.groupMeta}>
-                <span><strong>{group.totalTps.toFixed(1)}</strong> msg/s</span>
-                <span><strong>{group.totalActiveRoutes}</strong>/{group.totalRoutes} routes</span>
-                <span>
-                  <StatusDot
-                    variant={
-                      appHealth(group) === 'success'
-                        ? 'live'
-                        : appHealth(group) === 'warning'
-                          ? 'stale'
-                          : 'dead'
-                    }
-                  />
-                </span>
-              </div>
-            }
-            footer={
-              group.deadCount > 0 ? (
-                <div className={styles.alertBanner}>
-                  <span className={styles.alertIcon}>&#9888;</span>
+      {viewMode === 'expanded' || isFullWidth ? (
+        <div className={isFullWidth ? styles.groupGridSingle : styles.groupGrid}>
+          {groups.map((group) => (
+            <GroupCard
+              key={group.appId}
+              title={group.appId}
+              accent={appHealth(group)}
+              headerRight={
+                <Badge
+                  label={`${group.liveCount}/${group.instances.length} LIVE`}
+                  color={appHealth(group)}
+                  variant="filled"
+                />
+              }
+              meta={
+                <div className={styles.groupMeta}>
+                  <span><strong>{group.totalTps.toFixed(1)}</strong> msg/s</span>
+                  <span><strong>{group.totalActiveRoutes}</strong>/{group.totalRoutes} routes</span>
                   <span>
-                    Single point of failure &mdash;{' '}
-                    {group.deadCount === group.instances.length
-                      ? 'no redundancy'
-                      : `${group.deadCount} dead instance${group.deadCount > 1 ? 's' : ''}`}
+                    <StatusDot
+                      variant={
+                        appHealth(group) === 'success'
+                          ? 'live'
+                          : appHealth(group) === 'warning'
+                            ? 'stale'
+                            : 'dead'
+                      }
+                    />
                   </span>
                 </div>
-              ) : undefined
-            }
-          >
-            <DataTable<AgentInstance & { id: string }>
-              columns={instanceColumns as Column<AgentInstance & { id: string }>[]}
-              data={group.instances.map(i => ({ ...i, id: i.instanceId }))}
-              onRowClick={handleInstanceClick}
-              pageSize={50}
-              flush
-            />
-          </GroupCard>
-        ))}
-      </div>
+              }
+              footer={
+                group.deadCount > 0 ? (
+                  <div className={styles.alertBanner}>
+                    <span className={styles.alertIcon}>&#9888;</span>
+                    <span>
+                      Single point of failure &mdash;{' '}
+                      {group.deadCount === group.instances.length
+                        ? 'no redundancy'
+                        : `${group.deadCount} dead instance${group.deadCount > 1 ? 's' : ''}`}
+                    </span>
+                  </div>
+                ) : undefined
+              }
+            >
+              <DataTable<AgentInstance & { id: string }>
+                columns={instanceColumns as Column<AgentInstance & { id: string }>[]}
+                data={group.instances.map(i => ({ ...i, id: i.instanceId }))}
+                onRowClick={handleInstanceClick}
+                pageSize={50}
+                flush
+              />
+            </GroupCard>
+          ))}
+        </div>
+      ) : (
+        <div className={styles.compactGrid}>
+          {groups.map((group) =>
+            expandedApps.has(group.appId) ? (
+              <div key={group.appId} className={styles.compactGridExpanded}>
+                <GroupCard
+                  title={group.appId}
+                  accent={appHealth(group)}
+                  headerRight={
+                    <div style={{ display: 'flex', alignItems: 'center', gap: 8 }}>
+                      <Badge
+                        label={`${group.liveCount}/${group.instances.length} LIVE`}
+                        color={appHealth(group)}
+                        variant="filled"
+                      />
+                      <button
+                        className={styles.collapseBtn}
+                        onClick={() => toggleAppExpanded(group.appId)}
+                        title="Collapse"
+                      >
+                        <ChevronDown size={14} />
+                      </button>
+                    </div>
+                  }
+                  meta={
+                    <div className={styles.groupMeta}>
+                      <span><strong>{group.totalTps.toFixed(1)}</strong> msg/s</span>
+                      <span><strong>{group.totalActiveRoutes}</strong>/{group.totalRoutes} routes</span>
+                      <span>
+                        <StatusDot
+                          variant={
+                            appHealth(group) === 'success'
+                              ? 'live'
+                              : appHealth(group) === 'warning'
+                                ? 'stale'
+                                : 'dead'
+                          }
+                        />
+                      </span>
+                    </div>
+                  }
+                  footer={
+                    group.deadCount > 0 ? (
+                      <div className={styles.alertBanner}>
+                        <span className={styles.alertIcon}>&#9888;</span>
+                        <span>
+                          Single point of failure &mdash;{' '}
+                          {group.deadCount === group.instances.length
+                            ? 'no redundancy'
+                            : `${group.deadCount} dead instance${group.deadCount > 1 ? 's' : ''}`}
+                        </span>
+                      </div>
+                    ) : undefined
+                  }
+                >
+                  <DataTable<AgentInstance & { id: string }>
+                    columns={instanceColumns as Column<AgentInstance & { id: string }>[]}
+                    data={group.instances.map(i => ({ ...i, id: i.instanceId }))}
+                    onRowClick={handleInstanceClick}
+                    pageSize={50}
+                    flush
+                  />
+                </GroupCard>
+              </div>
+            ) : (
+              <CompactAppCard
+                key={group.appId}
+                group={group}
+                onExpand={() => toggleAppExpanded(group.appId)}
+              />
+            ),
+          )}
+        </div>
+      )}
 
       {/* Log + Timeline side by side */}
       <div className={styles.bottomRow}>