Base:||: A7   |   %   |   %   |   %   |
          D7   |   %   |   A7  |   %   |
         E7   |   D7  |   A7  |   E7 :||

Legenda:
%   = Repetir o mesmo acorde do compasso anterior.
:|| = (Ritornello) Retornar do começo ou do símbolo oposto ||:

 Tablatura:   A7
E|------------------------------------------|
B|------------------------------------------|
G|------------------------------------------|   (4x)
D|-2---2-4---4-2---2-4---4------------------|
A|-0---0-0---0-0---0-0---0------------------|
E|------------------------------------------|
PM ↓   ↓ ↓   ↓ ↓   ↓ ↓   ↓
    D7
E|------------------------------------------|
B|------------------------------------------|
G|-2---2-4---4-2---2-4---4------------------|   (2x)
D|-0---0-0---0-0---0-0---0------------------|
A|------------------------------------------|
E|------------------------------------------|
PM ↓   ↓ ↓   ↓ ↓   ↓ ↓   ↓
    A7
E|------------------------------------------|
B|------------------------------------------|
G|------------------------------------------|   (2x)
D|-2---2-4---4-2---2-4---4------------------|
A|-0---0-0---0-0---0-0---0------------------|
E|------------------------------------------|
PM ↓   ↓ ↓   ↓ ↓   ↓ ↓   ↓
    E7
E|------------------------------------------|
B|------------------------------------------|
G|------------------------------------------|
D|------------------------------------------|
A|-2---2-4---4-2---2-4---4------------------|
E|-0---0-0---0-0---0-0---0------------------|
PM ↓   ↓ ↓   ↓ ↓   ↓ ↓   ↓
    D7
E|------------------------------------------|
B|------------------------------------------|
G|-2---2-4---4-2---2-4---4------------------|   (2x)
D|-0---0-0---0-0---0-0---0------------------|
A|------------------------------------------|
E|------------------------------------------|
PM ↓   ↓ ↓   ↓ ↓   ↓ ↓   ↓
    A7
E|------------------------------------------|
B|------------------------------------------|
G|------------------------------------------|
D|-2---2-4---4-2---2-4---4------------------|
A|-0---0-0---0-0---0-0---0------------------|
E|------------------------------------------|
PM ↓   ↓ ↓   ↓ ↓   ↓ ↓   ↓
    E7
E|------------------------------------------|
B|------------------------------------------|
G|------------------------------------------|
D|------------------------------------------|
A|-2---2-4---4-2---2-4---4------------------|
E|-0---0-0---0-0---0-0---0------------------|
PM ↓   ↓ ↓   ↓ ↓   ↓ ↓   ↓

Retornar e repetir do começo quantas vezes quizer!

Esse riff pode ter inúmeras variações legais.
Olha só alguns exemplos:
Variação 1:
    A7
E|------------------------------------------|
B|------------------------------------------|
G|------------------------------------------|
D|-2---2-4---4-5---5-4---4------------------|
A|-0---0-0---0-0---0-0---0------------------|
E|------------------------------------------|
PM ↓   ↓ ↓   ↓ ↓   ↓ ↓   ↓
Variação 2:
    A7
E|------------------------------------------|
B|------------------------------------------|
G|------------------------------------------|
D|-2---2-4---4-2---2-----2------------------|
A|-0---0-0---0-0---0-3h4--------------------|
E|------------------------------------------|
PM ↓   ↓ ↓   ↓ ↓   ↓ ↓   ↑
Variação 3:
    A7
E|------------------------------------------|
B|------------------------------------------|
G|------------------------------------------|
D|-2---2-4---4-2----------------------------|
A|-0---0-0---0-0----------------------------|
E|-----------------0-3-0-3------------------|
PM ↓   ↓ ↓   ↓ ↓   ↓ ↓ ↓ ↓