Heart rate and HRV tracking, explained day by day

What Day's Heart shows

The first card on the Heart tab is Day's Heart, a grid of six tiles for the selected day: minimum, maximum and walking heart rate in beats per minute, resting heart rate, HRV in milliseconds, and blood oxygen (SpO2) as a percentage. Each tile opens its own detail screen, and every detail screen has a full history view you can switch between week, month, six months and year.

Because the whole app follows the day you pick, you can step back to any past day from the top bar or the Health Calendar and see that day's heart numbers exactly as they were.

• Resting Heart Rate - the heart rate your body settles to at rest, with zones labelled from Athletic to Elevated.
• HRV Analysis - the day's readings, a Throughout the Day chart, a Time of Day breakdown (night, morning, afternoon, evening) and a 7-day trend.
• Walking Heart Rate - how hard your heart works during ordinary walking, labelled from Needs Improvement to Excellent.
• Day's Heart Rate Range - your lowest and highest heart rate, the gap between them, and a label for the day's peak from Resting Day to Peak Effort.
• Blood Oxygen - your SpO2 readings, labelled Normal, Low or Very Low.

Why resting heart rate and HRV matter

Resting heart rate and HRV are two of the simplest windows into how your body is coping. As aerobic fitness improves, the heart tends to pump more blood with each beat, so resting heart rate usually drifts down over months of consistent training. In the short term, a resting heart rate that sits higher than usual for several days often goes along with poor sleep, accumulated fatigue, alcohol, heat, stress or the start of feeling unwell.

HRV measures the small variations in time between heartbeats. Higher HRV, compared with your own usual level, generally reflects a nervous system that is relaxed and recovered. Lower HRV tends to show up after hard training, short nights, stress or illness. HRV varies a lot between people, so the most useful comparison is you against yourself, not against someone else's number.

Walking heart rate adds an everyday fitness signal: if the same walk costs your heart fewer beats over time, your cardiovascular fitness is likely improving.

FitRest is a wellness app, not a medical device, and it does not diagnose or treat any condition. If a heart reading worries you, talk to a doctor.

Trends and Advanced Heart Analysis

One day of heart data is noisy. The Daily Heart Rate Trends card shows a day-by-day band from your lowest to highest heart rate with an average line through it, so you can scrub along and see which days ran hot. A range picker switches between the last 7, 14 or 30 days, and the card adds averages for the window and a one-line takeaway.

Advanced Heart Analysis adds two more cards on the same windows: Heart Rate Variability, with each day's minimum, average and maximum in milliseconds, and Resting Heart Rate, day by day. Together they make slow changes visible, such as resting heart rate easing down during a training block or HRV dipping through a stressful week.

Heart Signals: what changed against your normal

Heart Signals is a short card that answers one question: what changed compared with your usual? It shows up to three headlines, such as resting heart rate running higher than usual several days in a row, HRV sitting well below your normal, or a shallow overnight heart rate dip. When nothing stands out, it simply says all heart signals look normal.

The detail screen adds an Overnight HR Dip view, comparing your average heart rate while asleep with your daytime average, and a Caffeine and Your HRV view that compares your overnight HRV on lighter and heavier caffeine days using the drinks you log in FitRest. The app frames all of this as an early nudge to rest, hydrate and sleep, not a diagnosis.