Horizontal file concatenation

Hi,
is there a way to concatenate two files horizontally?

Starting from

```
field1,field2
0,a
1,b
3,a
```

and

```
field3,field4
0,a
1,b
3,a
```

obtain

```
field1,field2,field3,field4
0,a,0,a
1,b,1,b
3,a,3,a
```

Thank you