diff --git a/phys2denoise/metrics/__init__.py b/phys2denoise/metrics/__init__.py
index 57eeef1..71e03dc 100644
--- a/phys2denoise/metrics/__init__.py
+++ b/phys2denoise/metrics/__init__.py
@@ -1,4 +1,5 @@
 """Metrics derived from physiological signals."""
+
 from .cardiac import cardiac_phase, heart_beat_interval, heart_rate_variability
 from .chest_belt import (
     env,
diff --git a/phys2denoise/metrics/cardiac.py b/phys2denoise/metrics/cardiac.py
index 40ebc47..2ebf179 100644
--- a/phys2denoise/metrics/cardiac.py
+++ b/phys2denoise/metrics/cardiac.py
@@ -1,4 +1,5 @@
 """Denoising metrics for cardio recordings."""
+
 import numpy as np
 
 from .. import references
diff --git a/phys2denoise/metrics/chest_belt.py b/phys2denoise/metrics/chest_belt.py
index eeeb08a..17ec712 100644
--- a/phys2denoise/metrics/chest_belt.py
+++ b/phys2denoise/metrics/chest_belt.py
@@ -1,4 +1,5 @@
 """Denoising metrics for chest belt recordings."""
+
 import numpy as np
 import pandas as pd
 from scipy.interpolate import interp1d
diff --git a/phys2denoise/metrics/responses.py b/phys2denoise/metrics/responses.py
index aabcec9..e4abdaa 100644
--- a/phys2denoise/metrics/responses.py
+++ b/phys2denoise/metrics/responses.py
@@ -1,4 +1,5 @@
 """Miscellaneous utility functions for metric calculation."""
+
 import logging
 
 import numpy as np
diff --git a/phys2denoise/metrics/utils.py b/phys2denoise/metrics/utils.py
index 34fb21b..2faed26 100644
--- a/phys2denoise/metrics/utils.py
+++ b/phys2denoise/metrics/utils.py
@@ -1,4 +1,5 @@
 """Miscellaneous utility functions for metric calculation."""
+
 import logging
 
 import numpy as np
diff --git a/phys2denoise/references.py b/phys2denoise/references.py
index cb01db5..98dc75a 100644
--- a/phys2denoise/references.py
+++ b/phys2denoise/references.py
@@ -1,4 +1,5 @@
 """References to be imported and injected throughout the package."""
+
 from .due import Doi
 
 BIRN_2006 = Doi("10.1016/j.neuroimage.2006.02.048")
diff --git a/phys2denoise/tests/test_metrics_cardiac.py b/phys2denoise/tests/test_metrics_cardiac.py
index bb10d76..a93fc3b 100644
--- a/phys2denoise/tests/test_metrics_cardiac.py
+++ b/phys2denoise/tests/test_metrics_cardiac.py
@@ -1,4 +1,5 @@
 """Tests for phys2denoise.metrics.cardiac."""
+
 import numpy as np
 
 from phys2denoise.metrics import cardiac
diff --git a/phys2denoise/tests/test_metrics_chest_belt.py b/phys2denoise/tests/test_metrics_chest_belt.py
index 1250d85..286b6fa 100644
--- a/phys2denoise/tests/test_metrics_chest_belt.py
+++ b/phys2denoise/tests/test_metrics_chest_belt.py
@@ -1,4 +1,5 @@
 """Tests for phys2denoise.metrics.chest_belt."""
+
 import numpy as np
 from pytest import mark