diff --git a/withings_api/common.py b/withings_api/common.py
index 27f6c95..e334b86 100644
--- a/withings_api/common.py
+++ b/withings_api/common.py
@@ -558,9 +558,9 @@ class HeartBloodPressure(ConfiguredBaseModel):
 class HeartListSerie(ConfiguredBaseModel):
     """HeartListSerie"""
 
-    ecg: HeartListECG
+    ecg: Optional[HeartListECG] = None
 
-    heart_rate: int
+    heart_rate: Optional[int] = None
     timestamp: ArrowType
     model: HeartModel