How to Calculate Heart Rate a Level Biology

Calculate beats per minute using the Cardiac Cycle or Cardiac Output formula.

Method 1: Using Cardiac Cycle Time

Use this method when you have a pressure graph or ECG trace showing the time for one complete beat.

Method 2: Using Cardiac Output Formula

Based on the A Level formula: Cardiac Output = Stroke Volume × Heart Rate

function calculateByCycle() { var cycle = document.getElementById("cycleLength").value; var resultDiv = document.getElementById("cycleResult"); if (cycle > 0) { var hr = 60 / cycle; resultDiv.innerHTML = "Heart Rate: " + hr.toFixed(1) + " bpm"; resultDiv.style.color = "#0073aa"; } else { resultDiv.innerHTML = "Please enter a valid cycle length."; resultDiv.style.color = "red"; } } function calculateByCO() { var co = document.getElementById("cardiacOutput").value; var sv = document.getElementById("strokeVolume").value; var resultDiv = document.getElementById("coResult"); if (co > 0 && sv > 0) { var hr = co / sv; resultDiv.innerHTML = "Heart Rate: " + hr.toFixed(1) + " bpm"; resultDiv.style.color = "#d63031"; } else { resultDiv.innerHTML = "Please enter valid CO and SV values."; resultDiv.style.color = "red"; } }

How to Calculate Heart Rate in A Level Biology

In A Level Biology, particularly within the Exchange and Transport modules (OCR, AQA, Edexcel), you are frequently required to calculate heart rate from physiological data. There are two primary ways examiners will test this skill.

1. Calculation from a Cardiac Cycle Graph

You may be provided with a pressure-volume graph or an ECG trace. To find the heart rate, you must first identify the duration of one complete cardiac cycle. This is usually the time between two identical points on the graph (e.g., from the start of atrial systole in one beat to the start of atrial systole in the next).

Heart Rate (bpm) = 60 / Time for one cycle (seconds)

Example: If one cardiac cycle on a graph lasts 0.75 seconds:
60 / 0.75 = 80 beats per minute (bpm).

2. The Cardiac Output Formula

The relationship between the volume of blood pumped and the speed of the heart is defined by the Cardiac Output formula. You are often given two variables and asked to find the third.

• Cardiac Output (CO): The total volume of blood pumped by one ventricle in one minute (usually cm³ min⁻¹).
• Stroke Volume (SV): The volume of blood pumped out of the left ventricle during one contraction (cm³).
• Heart Rate (HR): The number of beats per minute (bpm).

Cardiac Output = Stroke Volume × Heart Rate

To find the heart rate, rearrange the formula: Heart Rate = Cardiac Output / Stroke Volume.

Common Exam Pitfalls to Avoid

• Units: Ensure your Cardiac Output is in cm³ per minute. If the exam provides it in dm³ per minute, multiply by 1000 first.
• Graph Reading: When reading time from the x-axis, check the scale carefully. A single small square might represent 0.02 or 0.04 seconds depending on the grid.
• Logic Check: A resting human heart rate is typically between 60 and 100 bpm. During exercise, it may rise to 150-200 bpm. If your calculation results in 5 bpm or 5000 bpm, re-check your math!