private List<string> readRow(IRow row)
{
    var rs = new List<string>();

    // Since there would be no emtpy cell,
    // we start from the left-most cell and read until the end.
    for (int colIndex = 0; colIndex < row.LastCellNum; colIndex++)
    {
        var cell = row.GetCell(colIndex);

        // Get the value of this cell, whether it is part of a merged cell or not.
        var cellValue = getCellValue(cell);

        rs.Add(cellValue);
    }
    return rs;
}

private string getCellValue(ICell cell)
{
    var dataFormatter = new DataFormatter(CultureInfo.CurrentCulture);

    // If this is not part of a merge cell,
    // just get this cell's value like normal.
    if (!cell.IsMergedCell)
    {
        return dataFormatter.FormatCellValue(cell);
    }

    // Otherwise, we need to find the value of this merged cell.
    else
    {
        // Get current sheet.
        var currentSheet = cell.Sheet;

        // Loop through all merge regions in this sheet.
        for (int i = 0; i < currentSheet.NumMergedRegions; i++)
        {
            var mergeRegion = currentSheet.GetMergedRegion(i);

            // If this merged region contains this cell.
            if (mergeRegion.FirstRow <= cell.RowIndex && cell.RowIndex <= mergeRegion.LastRow &&
                mergeRegion.FirstColumn <= cell.ColumnIndex && cell.ColumnIndex <= mergeRegion.LastColumn)
            {
                // Find the top-most and left-most cell in this region.
                var firstRegionCell = currentSheet.GetRow(mergeRegion.FirstRow)
                                        .GetCell(mergeRegion.FirstColumn);

                // And return its value.
                return dataFormatter.FormatCellValue(firstRegionCell);
            }
        }
        // This should never happen.
        throw new Exception("Cannot find this cell in any merged region");
    }
}

// And return its value.
                    return dataFormatter.FormatCellValue(firstRegionCell);
                }
                else
                    return dataFormatter.FormatCellValue(cell); //return cell if isMerge is true but not in range cells