diff --git a/client/src/callbacks.rs b/client/src/callbacks.rs
index c846d88ae..a75791dad 100644
--- a/client/src/callbacks.rs
+++ b/client/src/callbacks.rs
@@ -32,7 +32,7 @@ use crate::subscription::MonitoredItem;
 pub trait OnSubscriptionNotification {
     /// Called by the subscription after a `DataChangeNotification`. The default implementation
     /// does nothing.
-    fn on_data_change(&mut self, _data_change_items: Vec<&MonitoredItem>) {}
+    fn on_data_change(&mut self, _data_change_items: &Vec<&MonitoredItem>) {}
 
     /// Called by the subscription after a `EventNotificationList`. The notifications contained within
     /// are individual `EventFieldList` structs filled from the select clause criteria from when the
@@ -64,11 +64,11 @@ pub trait OnSessionClosed {
 /// a data change occurs.
 pub struct DataChangeCallback {
     /// The actual call back
-    cb: Box<dyn Fn(Vec<&MonitoredItem>) + Send + Sync + 'static>,
+    cb: Box<dyn Fn(&Vec<&MonitoredItem>) + Send + Sync + 'static>,
 }
 
 impl OnSubscriptionNotification for DataChangeCallback {
-    fn on_data_change(&mut self, data_change_items: Vec<&MonitoredItem>) {
+    fn on_data_change(&mut self, data_change_items: &Vec<&MonitoredItem>) {
         (self.cb)(data_change_items);
     }
 }
@@ -77,7 +77,7 @@ impl DataChangeCallback {
     /// Constructs a callback from the supplied function
     pub fn new<CB>(cb: CB) -> Self
     where
-        CB: Fn(Vec<&MonitoredItem>) + Send + Sync + 'static,
+        CB: Fn(&Vec<&MonitoredItem>) + Send + Sync + 'static,
     {
         Self { cb: Box::new(cb) }
     }
diff --git a/client/src/lib.rs b/client/src/lib.rs
index 93ff6e43a..9481d91ab 100644
--- a/client/src/lib.rs
+++ b/client/src/lib.rs
@@ -79,7 +79,7 @@
 //!
 //! fn print_value(item: &MonitoredItem) {
 //!    let node_id = &item.item_to_monitor().node_id;
-//!    let data_value = item.value();
+//!    let data_value = item.last_value();
 //!    if let Some(ref value) = data_value.value {
 //!        println!("Item \"{}\", Value = {:?}", node_id, value);
 //!    } else {
diff --git a/client/src/session.rs b/client/src/session.rs
index 235516b0d..3cfa80b5a 100644
--- a/client/src/session.rs
+++ b/client/src/session.rs
@@ -431,7 +431,7 @@ impl Session {
                                         client_handle: item.client_handle(),
                                         sampling_interval: item.sampling_interval(),
                                         filter: ExtensionObject::null(),
-                                        queue_size: item.queue_size(),
+                                        queue_size: item.queue_size() as u32,
                                         discard_oldest: true,
                                     },
                                 })
diff --git a/client/src/subscription.rs b/client/src/subscription.rs
index a9fcd0fce..368936b8c 100644
--- a/client/src/subscription.rs
+++ b/client/src/subscription.rs
@@ -50,7 +50,7 @@ pub struct MonitoredItem {
     // The thing that is actually being monitored - the node id, attribute, index, encoding.
     item_to_monitor: ReadValueId,
     /// Queue size
-    queue_size: u32,
+    queue_size: usize,
     /// Discard oldest
     discard_oldest: bool,
     /// Monitoring mode
@@ -58,7 +58,10 @@ pub struct MonitoredItem {
     /// Sampling interval
     sampling_interval: f64,
     /// Last value of the item
-    value: DataValue,
+    last_value: DataValue,
+    /// A list of all values received in the last data change notification. This list is cleared immediately
+    /// after the data change notification.
+    values: Vec<DataValue>,
     /// Triggered items
     triggered_items: BTreeSet<u32>,
 }
@@ -67,7 +70,7 @@ impl MonitoredItem {
     pub fn new(client_handle: u32) -> MonitoredItem {
         MonitoredItem {
             id: 0,
-            queue_size: 0,
+            queue_size: 1,
             sampling_interval: 0.0,
             item_to_monitor: ReadValueId {
                 node_id: NodeId::null(),
@@ -77,7 +80,8 @@ impl MonitoredItem {
             },
             monitoring_mode: MonitoringMode::Reporting,
             discard_oldest: false,
-            value: DataValue::null(),
+            last_value: DataValue::null(),
+            values: Vec::with_capacity(1),
             client_handle,
             triggered_items: BTreeSet::new(),
         }
@@ -99,12 +103,27 @@ impl MonitoredItem {
         self.sampling_interval
     }
 
-    pub fn queue_size(&self) -> u32 {
+    pub fn queue_size(&self) -> usize {
         self.queue_size
     }
 
-    pub fn value(&self) -> &DataValue {
-        &self.value
+    pub fn last_value(&self) -> &DataValue {
+        &self.last_value
+    }
+
+    pub fn values(&self) -> &Vec<DataValue> {
+        &self.values
+    }
+
+    pub fn clear_values(&mut self) {
+        self.values.clear();
+    }
+
+    pub fn append_new_value(&mut self, value: DataValue) {
+        if self.values.len() == self.queue_size {
+            let _ = self.values.pop();
+            self.values.push(value);
+        }
     }
 
     pub fn monitoring_mode(&self) -> MonitoringMode {
@@ -127,8 +146,12 @@ impl MonitoredItem {
         self.sampling_interval = value;
     }
 
-    pub(crate) fn set_queue_size(&mut self, value: u32) {
+    pub(crate) fn set_queue_size(&mut self, value: usize) {
         self.queue_size = value;
+        if self.queue_size > self.values.capacity() {
+            self.values
+                .reserve(self.queue_size - self.values.capacity());
+        }
     }
 
     pub(crate) fn set_monitoring_mode(&mut self, monitoring_mode: MonitoringMode) {
@@ -272,7 +295,7 @@ impl Subscription {
             monitored_item.set_monitoring_mode(i.monitoring_mode);
             monitored_item.set_discard_oldest(i.discard_oldest);
             monitored_item.set_sampling_interval(i.sampling_interval);
-            monitored_item.set_queue_size(i.queue_size);
+            monitored_item.set_queue_size(i.queue_size as usize);
             monitored_item.set_item_to_monitor(i.item_to_monitor.clone());
 
             let client_handle = monitored_item.client_handle();
@@ -287,7 +310,7 @@ impl Subscription {
         items_to_modify.iter().for_each(|i| {
             if let Some(ref mut monitored_item) = self.monitored_items.get_mut(&i.id) {
                 monitored_item.set_sampling_interval(i.sampling_interval);
-                monitored_item.set_queue_size(i.queue_size);
+                monitored_item.set_queue_size(i.queue_size as usize);
             }
         });
     }
@@ -327,8 +350,9 @@ impl Subscription {
 
     pub(crate) fn on_data_change(&mut self, data_change_notifications: &[DataChangeNotification]) {
         let mut monitored_item_ids = HashSet::new();
-        for n in data_change_notifications {
+        data_change_notifications.iter().for_each(|n| {
             if let Some(ref monitored_items) = n.monitored_items {
+                monitored_item_ids.clear();
                 for i in monitored_items {
                     let monitored_item_id = {
                         let monitored_item_id = self.monitored_item_id_from_handle(i.client_handle);
@@ -338,21 +362,29 @@ impl Subscription {
                         *monitored_item_id.as_ref().unwrap()
                     };
                     let monitored_item = self.monitored_items.get_mut(&monitored_item_id).unwrap();
-                    monitored_item.value = i.value.clone();
+                    monitored_item.last_value = i.value.clone();
+                    monitored_item.values.push(i.value.clone());
                     monitored_item_ids.insert(monitored_item_id);
                 }
+                if !monitored_item_ids.is_empty() {
+                    let data_change_items: Vec<&MonitoredItem> = monitored_item_ids
+                        .iter()
+                        .map(|id| self.monitored_items.get(&id).unwrap())
+                        .collect();
+
+                    {
+                        // Call the call back with the changes we collected
+                        let mut cb = trace_lock_unwrap!(self.notification_callback);
+                        cb.on_data_change(&data_change_items);
+                    }
+
+                    // Clear the values
+                    monitored_item_ids.iter().for_each(|id| {
+                        let m = self.monitored_items.get_mut(&id).unwrap();
+                        m.clear_values();
+                    });
+                }
             }
-        }
-
-        if !monitored_item_ids.is_empty() {
-            let data_change_items: Vec<&MonitoredItem> = monitored_item_ids
-                .iter()
-                .map(|id| self.monitored_items.get(&id).unwrap())
-                .collect();
-
-            // Call the call back with the changes we collected
-            let mut cb = trace_lock_unwrap!(self.notification_callback);
-            cb.on_data_change(data_change_items);
-        }
+        });
     }
 }
diff --git a/samples/mqtt-client/src/main.rs b/samples/mqtt-client/src/main.rs
index 1e242eacb..b595dde21 100644
--- a/samples/mqtt-client/src/main.rs
+++ b/samples/mqtt-client/src/main.rs
@@ -150,7 +150,7 @@ fn subscription_loop(
                 let tx = tx.lock().unwrap();
                 items.iter().for_each(|item| {
                     let node_id = item.item_to_monitor().node_id.clone();
-                    let value = item.value().clone();
+                    let value = item.last_value().clone();
                     let _ = tx.send((node_id, value));
                 });
             }),
diff --git a/samples/simple-client/src/main.rs b/samples/simple-client/src/main.rs
index 5834a03a4..b7fd9239e 100644
--- a/samples/simple-client/src/main.rs
+++ b/samples/simple-client/src/main.rs
@@ -118,7 +118,7 @@ fn subscribe_to_variables(session: Arc<RwLock<Session>>, ns: u16) -> Result<(),
 
 fn print_value(item: &MonitoredItem) {
     let node_id = &item.item_to_monitor().node_id;
-    let data_value = item.value();
+    let data_value = item.last_value();
     if let Some(ref value) = data_value.value {
         println!("Item \"{}\", Value = {:?}", node_id, value);
     } else {
diff --git a/samples/web-client/src/main.rs b/samples/web-client/src/main.rs
index f62c1030a..5a67c57e5 100644
--- a/samples/web-client/src/main.rs
+++ b/samples/web-client/src/main.rs
@@ -1,4 +1,5 @@
 // OPCUA for Rust
+// OPCUA for Rust
 // SPDX-License-Identifier: MPL-2.0
 // Copyright (C) 2017-2020 Adam Lock
 
@@ -415,7 +416,7 @@ impl OPCUASession {
                         DataChangeEvent {
                             node_id: item_to_monitor.node_id.clone().into(),
                             attribute_id: item_to_monitor.attribute_id,
-                            value: item.value().clone(),
+                            value: item.last_value().clone(),
                         }
                     })
                     .collect::<Vec<_>>();