Sensebridge is a little board that logs up to 61831 heart beats, about 14 hours of data. It is based on a atmega 168, a Real Time Clock, and 512 Kbit EEPROM. And it’s released open source.
The Heart Spark is a heart-shaped pendant which flashes little lights (light emitting diodes, LEDs) in time with your heart beat. A polar chest strap with transmitter (sold separately) is used to measure your heart beat, which is transmitted wirelessly to the pendant. An arduino-compatible circuit captures each beat as it happens and flashes LEDs (later versions will log data to an onboard EEPROM – see below). The pendant is carefully designed to maximize its visual appeal, including symmetry and optionally a high-gloss epoxy coating (as pictured to the right). A CR2032 coin-cell battery provides 8+ hours of battery life. Two small switches on the back allow selection of operating mode: