Cardiac Insight, a Bellevue, Wash. startup that makes lightweight disposable electrocardiogram (ECG) sensors and software to monitor patients’ heartbeats, has raised $8 million in funding amid a period of rapid customer growth.

SeaChange Fund, which invests exclusively in Pacific Northwest startups, was the only named investor in the Series D round. The fund said it accounted for $500,000 to $900,000 in the round.

Cardea Solo is Cardiac Insight’s flagship device, and it detects irregular heartbeats, also known as arrhythmia. Patients wear the device for a week, and then come back to the doctor. A small chip is removed from the wearable sensor and processed immediately through software made by Cardiac Insight, letting doctors give an on-the-spot diagnosis.

Cardiac Insight sells the device to physicians and cardiac experts. The company is seeing 100 percent year-over-year sales growth in the U.S., increasing its customer base and moving into new “global verticals,” CEO Brad Harlow said.

The startup has just shy of 30 people, and it is ramping up hiring of sales and marketing staff.