4iiii's chest-strap heart rate monitor, built to sit alongside a power meter: watts show your output, heart rate shows what that output costs you. It sends over both ANT+ and Bluetooth and runs 540+ hours on a CR2032 coin cell.

Highlights

• ANT+ and Bluetooth, for head units, watches, phones and indoor training apps
• 540+ hours from one CR2032 coin cell
• IPX7 water resistance
• Fits chests from 66 to 132 cm
• Heart rate range 30–240 bpm at 1 bpm resolution
• Set up and update through the 4iiii app

Power and heart rate together

Paired with a 4iiii power meter, the Viiiiva shows both sides of an effort: external output in watts and your body's response in beats per minute. Together they help you set training zones and track fitness over time, outdoors or on the trainer in Zwift.

Wearing and care

Wet the strap's conductive pads with a few drops of water, then slide the pod down onto the connectors with the arrows on the back pointing up; worn upside down, it reads inaccurately. Sit the strap snug, just below the chest muscles, with the pod centred. It powers down after three minutes without a valid heart rate signal. Separate the pod and hand wash the strap in warm water with mild soap; never put it in a washing machine.

Compatibility & fit

Works with ANT+ and Bluetooth head units, watches and apps: the Viiiiva pairs ANT+ to ANT+ devices and Bluetooth to Bluetooth devices, with a typical range of 3 m. This is the current Viiiiva, with a slide-on pod; straps for the original snap-on Viiiiva are a different design.

Warning: This product contains a button/coin battery. Keep new and used batteries out of reach of children. Swallowing can cause serious injury or death within hours. Seek medical attention immediately if a battery may have been swallowed or placed inside any part of the body.