Heresy

St. Thomas Aquinas defines heresy as:

"a species of infidelity in men who, having professed the faith of Christ, corrupt its dogmas. The right Christian faith consists in giving one's voluntary assent to Christ in all that truly belongs to His teaching. There are, therefore, two ways of deviating from Christianity: the one by refusing to believe in Christ Himself, which is the way of infidelity, common to Pagans and Jews; the other by restricting belief to certain points of Christ's doctrine selected and fashioned at pleasure, which is the way of heretics. The subject-matter of both faith and heresy is, therefore, the deposit of the faith, that is, the sum total of truths revealed in Scripture and Tradition as proposed to our belief by the Church. The believer accepts the whole deposit as proposed by the Church; the heretic accepts only such parts of it as commend themselves to his own approval.”

(Summa Theologica, II-II:11:1; Summa written 1265-1274) Heresy definition - NewAdvent.org

Clicking on the Early Church Father's name or on the work will take you to The Catholic Encyclopedia at NewAdvent.org

Alexander of Alexandria  
Epistles on the Arian Heresy and the Deposition of Arius

Alexander of Lycopolis
Of the Manicheans

Ambrose (340-397)  
Sermon against Auxentius

Archelaus
Acts of the Disputation with the Heresiarch Manes

Aristides the Philosopher
The Apology

Arnobius
Against the Heathen

Athanasius  
Against the Heathen
Deposition of Arius
Statement of Faith
Apologia Contra Arianos
Apologia ad Constantium
Apologia de Fuga
Four Discourses Against the Arians

Augustine of Hippo  
On the Morals of the Manichaeans
On Two Souls, Against the Manichaeans
Acts or Disputation Against Fortunatus the Manichaean
Against the Epistle of Manichaeus Called Fundamental
Reply to Faustus the Manichaean
Concerning the Nature of Good, Against the Manichaeans
On Baptism, Against the Donatists
Answer to Letters of Petilian, Bishop of Cirta
On the Proceedings of Pelagius
Against Two Letters of the Pelagians

Dionysius of Rome  
Against the Sabellians

Eusebius of Caesarea (c. 265-c. 340)
Church History

Gennadius of Marseilles
Illustrious Men (Supplement to Jerome)

Gregory of Nyssa  
Against Eunomius
Answer to Eunomius' Second Book
On the Holy Spirit (Against the Followers of Macedonius)
On "Not Three Gods" (To Ablabius)

Hippolytus  
The Refutation of All Heresies
Against Plato, On the Cause of the Universe
Against the Heresy of Noetus

Ignatius of Antioch  
Epistle to the Ephesians
Epistle to the Magnesians
Epistle to the Trallians
Epistle to the Romans
Epistle to the Philadelphians
Epistle to the Smyrnæans 

Irenaeus of Lyons  
Adversus haereses

Jerome  
To Pammachius Against John of Jerusalem
The Dialogue Against the Luciferians
Against Jovinianus
Against Vigilantius
Against the Pelagians

John Cassian (c. 360-c. 435)
On the Incarnation of the Lord (Against Nestorius)

Justin Martyr
First Apology
Second Apology
Dialogue with Trypho

Rufinus
Apology

Tertullian
The Apology
On Idolatry 
The Prescription Against Heretics
Against Marcion
Against Hermogenes
Against the Valentinians