diff --git a/beacon_node/operation_pool/src/lib.rs b/beacon_node/operation_pool/src/lib.rs
index 5842120c6cc..eceae5db36c 100644
--- a/beacon_node/operation_pool/src/lib.rs
+++ b/beacon_node/operation_pool/src/lib.rs
@@ -44,6 +44,7 @@ use types::{
     Epoch, EthSpec, ProposerSlashing, SignedBeaconBlock, SignedBlsToExecutionChange,
     SignedVoluntaryExit, Slot, SyncAggregate, SyncCommitteeContribution, Validator,
 };
+use rayon::prelude::*;
 
 type SyncContributions<T> = RwLock<HashMap<SyncAggregateId, Vec<SyncCommitteeContribution<T>>>>;
 
@@ -230,112 +231,120 @@ impl<T: EthSpec> OperationPool<T> {
         mut validity_filter: impl FnMut(&AttestationRef<'a, T>) -> bool + Send,
         num_valid: &mut i64,
         spec: &'a ChainSpec,
-    ) -> Vec<(&CompactAttestationData, CompactIndexedAttestation<T>)> {
-        let mut cliqued_atts: Vec<(&CompactAttestationData, CompactIndexedAttestation<T>)> = vec![];
-
+    ) -> Vec<(&CompactAttestationData, Vec<CompactIndexedAttestation<T>>)> {
         if let Some(AttestationDataMap {
-            aggregate_attestations,
-            unaggregate_attestations,
-        }) = all_attestations.get_attestation_map(checkpoint_key)
+                aggregate_attestations,
+                unaggregate_attestations,
+            }) = all_attestations.get_attestation_map(checkpoint_key)
         {
-            for (data, aggregates) in aggregate_attestations {
-                if data.slot + spec.min_attestation_inclusion_delay <= state.slot()
+            let mut cliques_from_aggregates: Vec<_> = aggregate_attestations.into_iter().filter(|(data, _)| {
+                data.slot + spec.min_attestation_inclusion_delay <= state.slot()
                     && state.slot() <= data.slot + T::slots_per_epoch()
-                {
-                    let aggregates: Vec<&CompactIndexedAttestation<T>> = aggregates
-                        .iter()
-                        .filter(|indexed| {
-                            validity_filter(&AttestationRef {
-                                checkpoint: checkpoint_key,
-                                data: &data,
-                                indexed,
-                            })
-                        })
-                        .collect();
-                    *num_valid += aggregates.len() as i64;
-
-                    // aggregate each cliques corresponding attestaiions
-                    let mut clique_aggregates: Vec<CompactIndexedAttestation<_>> = bron_kerbosch(&aggregates, is_compatible)
-                        .iter()
-                        .map(|clique| {
-                            clique.iter().skip(1).fold(aggregates[clique[0]].clone(), |mut acc, &ind| {
-                                acc.aggregate(&aggregates[ind]);
-                                acc
-                            }) 
+            })
+            .map(|(data, aggregates)| {
+                let aggregates: Vec<&CompactIndexedAttestation<T>> = aggregates
+                    .iter()
+                    .filter(|indexed| {
+                        validity_filter(&AttestationRef {
+                            checkpoint: checkpoint_key,
+                            data: &data,
+                            indexed,
                         })
-                        .collect();
-                    let mut indices_to_remove = Vec::new();
-                    clique_aggregates
-                        .sort_unstable_by(|a, b| a.attesting_indices.len().cmp(&b.attesting_indices.len()));
-                    for (index, clique) in clique_aggregates.iter().enumerate() {
-                        for bigger_clique in clique_aggregates.iter().skip(index + 1) {
-                            if clique
-                                .aggregation_bits
+                    })
+                    .collect();
+                *num_valid += aggregates.len() as i64;
+                (data, aggregates)
+            })
+            .collect::<Vec<(&CompactAttestationData, Vec<&CompactIndexedAttestation<_>>)>>()
+            .into_par_iter()
+            .map(|(data, aggregates)| {
+                // aggregate each cliques corresponding attestaiions
+                let mut clique_aggregates: Vec<CompactIndexedAttestation<_>> = bron_kerbosch(&aggregates, is_compatible)
+                    .iter()
+                    .map(|clique| {
+                        clique.iter().skip(1).fold(aggregates[clique[0]].clone(), |mut acc, &ind| {
+                            acc.aggregate(&aggregates[ind]);
+                            acc
+                        }) 
+                    })
+                .collect();
+                let mut indices_to_remove = Vec::new();
+                clique_aggregates
+                    .sort_unstable_by(|a, b| a.attesting_indices.len().cmp(&b.attesting_indices.len()));
+                for (index, clique) in clique_aggregates.iter().enumerate() {
+                    for bigger_clique in clique_aggregates.iter().skip(index + 1) {
+                        if clique
+                            .aggregation_bits
                                 .is_subset(&bigger_clique.aggregation_bits)
-                            {
-                                indices_to_remove.push(index);
-                                break;
-                            }
-                        }
-                    }
-
-                    for index in indices_to_remove.iter().rev() {
-                        clique_aggregates.swap_remove(*index);
+                                {
+                                    indices_to_remove.push(index);
+                                    break;
+                                }
                     }
+                }
 
-                    // aggregate unaggregate attestations into the clique aggregates
-                    // if compatible
-                    if let Some(unaggregate_attestations) = unaggregate_attestations.get(&data) {
-                        for attestation in unaggregate_attestations.iter().filter(|indexed| {
-                            validity_filter(&AttestationRef {
-                                checkpoint: checkpoint_key,
-                                data: &data,
-                                indexed,
-                            })
-                        }) {
-                            *num_valid += 1;
-                            for clique_aggregate in &mut clique_aggregates {
-                                if !clique_aggregate
-                                    .attesting_indices
+                for index in indices_to_remove.iter().rev() {
+                    clique_aggregates.swap_remove(*index);
+                }
+                (data, clique_aggregates)
+            })
+            .collect::<Vec<(&CompactAttestationData, Vec<CompactIndexedAttestation<_>>)>>()
+            .into_iter()
+            .map(|(data, mut clique_aggregates)| {
+                // aggregate unaggregate attestations into the clique aggregates
+                // if compatible
+                if let Some(unaggregate_attestations) = unaggregate_attestations.get(&data) {
+                    for attestation in unaggregate_attestations.iter().filter(|indexed| {
+                        validity_filter(&AttestationRef {
+                            checkpoint: checkpoint_key,
+                            data: &data,
+                            indexed,
+                        })
+                    }) {
+                        *num_valid += 1;
+                        for clique_aggregate in &mut clique_aggregates {
+                            if !clique_aggregate
+                                .attesting_indices
                                     .contains(&attestation.attesting_indices[0])
-                                {
-                                    clique_aggregate.aggregate(attestation);
-                                }
-                            }
+                                    {
+                                        clique_aggregate.aggregate(attestation);
+                                    }
                         }
                     }
-
-                    cliqued_atts
-                        .extend(clique_aggregates.into_iter().map(|indexed| (data, indexed)));
                 }
-            }
+                (data, clique_aggregates)
+            })
+            .collect();
+
             // include aggregated attestations from unaggregated attestations whose
             // attestation data doesn't appear in aggregated_attestations
-            for (data, attestations) in unaggregate_attestations {
-                if data.slot + spec.min_attestation_inclusion_delay <= state.slot()
-                    && state.slot() <= data.slot + T::slots_per_epoch()
-                {
-                    if !aggregate_attestations.contains_key(&data) {
-                        let mut valid_attestations = attestations.iter().filter(|indexed| {
-                            validity_filter(&AttestationRef {
-                                checkpoint: checkpoint_key,
-                                data: &data,
-                                indexed,
-                            })
+            unaggregate_attestations
+                .iter()
+                .filter(|(data, _)| {
+                    data.slot + spec.min_attestation_inclusion_delay <= state.slot()
+                        && state.slot() <= data.slot + T::slots_per_epoch()
+                        && !aggregate_attestations.contains_key(&data)
+                })
+                .for_each(|(data, unaggregates)| {
+                    let mut valid_attestations = unaggregates.iter().filter(|indexed| {
+                        validity_filter(&AttestationRef {
+                            checkpoint: checkpoint_key,
+                            data: &data,
+                            indexed,
+                        })
+                    });
+                    if let Some(att) = valid_attestations.next() {
+                        let mut att = att.clone();
+                        valid_attestations.for_each(|valid_att| {
+                            att.aggregate(valid_att)
                         });
-
-                        if let Some(first) = valid_attestations.next() {
-                            let mut agg = first.clone();
-                            for attestation in valid_attestations {
-                                agg.aggregate(&attestation);
-                            }
-                            cliqued_atts.push((data, agg));
-                        }
+                        cliques_from_aggregates.push((data, vec![att]))
                     }
-                }
-            }
+                });
+            cliques_from_aggregates
+        } else {
+            vec![]
         }
-        cliqued_atts
     }
 
     /// Get a list of attestations for inclusion in a block.
@@ -386,14 +395,17 @@ impl<T: EthSpec> OperationPool<T> {
 
         let prev_epoch_cliqued_atts = prev_epoch_cliqued_atts
             .iter()
-            .map(|(data, indexed)| AttestationRef {
-                checkpoint: &prev_epoch_key,
-                data,
-                indexed,
+            .map(|(data, atts)| {
+                atts.iter().map(|indexed| AttestationRef {
+                    checkpoint: &prev_epoch_key,
+                    data,
+                    indexed,
+                })
+                .filter_map(|att| {
+                    AttMaxCover::new(att, state, &reward_cache, total_active_balance, spec)
+                })
             })
-            .filter_map(|att| {
-                AttMaxCover::new(att, state, &reward_cache, total_active_balance, spec)
-            });
+            .flat_map(|att_max_cover| att_max_cover);
 
         let curr_epoch_cliqued_atts = self.get_clique_aggregate_attestations_for_epoch(
             &curr_epoch_key,
@@ -406,14 +418,17 @@ impl<T: EthSpec> OperationPool<T> {
 
         let curr_epoch_cliqued_atts = curr_epoch_cliqued_atts
             .iter()
-            .map(|(data, indexed)| AttestationRef {
-                checkpoint: &curr_epoch_key,
-                data,
-                indexed,
+            .map(|(data, atts)| {
+                atts.iter().map(|indexed| AttestationRef {
+                    checkpoint: &curr_epoch_key,
+                    data,
+                    indexed,
+                })
+                .filter_map(|att| {
+                    AttMaxCover::new(att, state, &reward_cache, total_active_balance, spec)
+                })
             })
-            .filter_map(|att| {
-                AttMaxCover::new(att, state, &reward_cache, total_active_balance, spec)
-            });
+            .flat_map(|att_max_cover| att_max_cover);
 
         let prev_epoch_limit = if let BeaconState::Base(base_state) = state {
             std::cmp::min(