The left three-atrial heart (LTH) is a rare congenital abnormality where the left auricle (LA) is divided into two chambers with an additional membrane. This article describes for the first time a clinical case of congenital heart defect with four atrial chambers. A 41-old man was hospitalized for newly diagnosed paroxysmal atrial fibrillation. On transthoracic echocardiogram (EchoCG), LA was considerably enlarged and divided into two equal interconnected parts with a membrane. Additional examination with contrast-enhanced EchoCG and computed tomography revealed two membranes dividing the LA into three chambers. Prediction for the patient was beneficial since there were no other developmental abnormalities of the heart, and the LA transmembrane pressure gradient (PG) was small. Data of literature on the incidence and prognosis of LTH are provided.