diff --git a/.betterer.results b/.betterer.results
index 42417c7ca52..0fc12f0c348 100644
--- a/.betterer.results
+++ b/.betterer.results
@@ -7072,10 +7072,10 @@ exports[`better eslint`] = {
     "public/app/features/transformers/calculateHeatmap/editor/helper.ts:2898656130": [
       [10, 37, 3, "Unexpected any. Specify a different type.", "193409811"]
     ],
-    "public/app/features/transformers/calculateHeatmap/heatmap.ts:2895010613": [
+    "public/app/features/transformers/calculateHeatmap/heatmap.ts:992367420": [
       [65, 9, 52, "Do not use any type assertions.", "3480700880"],
-      [306, 63, 29, "Do not use any type assertions.", "255738422"],
-      [306, 89, 3, "Unexpected any. Specify a different type.", "193409811"]
+      [321, 63, 29, "Do not use any type assertions.", "255738422"],
+      [321, 89, 3, "Unexpected any. Specify a different type.", "193409811"]
     ],
     "public/app/features/transformers/configFromQuery/ConfigFromQueryTransformerEditor.test.tsx:1060905279": [
       [44, 29, 21, "Do not use any type assertions.", "1548027068"]
diff --git a/public/app/features/transformers/calculateHeatmap/heatmap.ts b/public/app/features/transformers/calculateHeatmap/heatmap.ts
index af52aa0edfb..75313151d2b 100644
--- a/public/app/features/transformers/calculateHeatmap/heatmap.ts
+++ b/public/app/features/transformers/calculateHeatmap/heatmap.ts
@@ -244,9 +244,6 @@ export function prepBucketFrames(frames: DataFrame[]): DataFrame[] {
 export function calculateHeatmapFromData(frames: DataFrame[], options: HeatmapCalculationOptions): DataFrame {
   //console.time('calculateHeatmapFromData');
 
-  let xs: number[] = [];
-  let ys: number[] = [];
-
   // optimization
   //let xMin = Infinity;
   //let xMax = -Infinity;
@@ -254,6 +251,20 @@ export function calculateHeatmapFromData(frames: DataFrame[], options: HeatmapCa
   let xField: Field | undefined = undefined;
   let yField: Field | undefined = undefined;
 
+  let dataLen = 0;
+  // pre-allocate arrays
+  for (let frame of frames) {
+    // TODO: assumes numeric timestamps, ordered asc, without nulls
+    const x = frame.fields.find((f) => f.type === FieldType.time);
+    if (x) {
+      dataLen += frame.length;
+    }
+  }
+
+  let xs: number[] = Array(dataLen);
+  let ys: number[] = Array(dataLen);
+  let j = 0;
+
   for (let frame of frames) {
     // TODO: assumes numeric timestamps, ordered asc, without nulls
     const x = frame.fields.find((f) => f.type === FieldType.time);
@@ -268,8 +279,12 @@ export function calculateHeatmapFromData(frames: DataFrame[], options: HeatmapCa
     const xValues = x.values.toArray();
     for (let field of frame.fields) {
       if (field !== x && field.type === FieldType.number) {
-        xs = xs.concat(xValues);
-        ys = ys.concat(field.values.toArray());
+        const yValues = field.values.toArray();
+
+        for (let i = 0; i < xValues.length; i++, j++) {
+          xs[j] = xValues[i];
+          ys[j] = yValues[i];
+        }
 
         if (!yField) {
           yField = field;