diff --git a/Makefile b/Makefile
index db60e84..c567b36 100644
--- a/Makefile
+++ b/Makefile
@@ -30,7 +30,7 @@ endif
 
 # debug and release flags
 
-DEBUG_CFLAGS=-O0 -Og -ggdb3 ${WARNINGS} -fno-omit-frame-pointer -fsanitize=address -fsanitize=undefined \
+DEBUG_CFLAGS=-Og -ggdb3 ${WARNINGS} -fno-omit-frame-pointer -fsanitize=address -fsanitize=undefined \
   -fno-sanitize-recover=all -fstack-protector-strong -fstack-clash-protection -fno-common ${ADD_DBG_FLAGS} \
   -DCHECK_TYCHE_BUGS=1
 DEBUG_LDFLAGS=-fsanitize=address -fsanitize=undefined
@@ -45,7 +45,7 @@ endif
 RELEASE_CFLAGS=-O3 -flto=auto -march=native -mtune=native -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3 -fstack-protector-strong
 RELEASE_LDFLAGS=-flto=auto
 
-CFLAGS+=-std=c99 -fPIC -fvisibility=hidden
+CFLAGS+=-std=c99 -D_GNU_SOURCE -fPIC -fvisibility=hidden
 LDFLAGS+=
 
 
@@ -102,4 +102,4 @@ libtyche.a: lib/vm.o
 
 libtyche.so.${VERSION}: LDFLAGS += ${RELEASE_LDFLAGS}
 libtyche.so.${VERSION}: lib/vm.o
-	$(CC) -shared -o $@ -Wl,-soname,libfoo.so.${VERSION_MAJOR} $^ ${LDFLAGS}
\ No newline at end of file
+	$(CC) -shared -o $@ -Wl,-soname,libfoo.so.${VERSION_MAJOR} $^ ${LDFLAGS}
diff --git a/lib/heap.c b/lib/heap.c
index d943a3f..e6df048 100644
--- a/lib/heap.c
+++ b/lib/heap.c
@@ -1,23 +1,85 @@
 #include "stack.c"
 
 #include <stdlib.h>
+#include <string.h>
 
 #include "khash.h"
 
-typedef struct {
-} HeapValue;
-KHASH_MAP_INIT_INT(heap, HeapValue)
+typedef int HEAP_KEY;
+
+typedef enum {
+    TH_STRING, TH_ARRAY, TH_TABLE,
+} TYC_HEAP_TYPE;
 
 typedef struct {
-    khash_t(heap) *items;
+    TYC_HEAP_TYPE type;
+    union {
+        char* str;
+        // TODO - array and table
+    } value;
+} HeapValue;
+KHASH_MAP_INIT_INT(HEAP, HeapValue)
+
+typedef struct {
+    khash_t(HEAP) *items;
 } Heap;
 
 static void heap_init(Heap* h)
 {
-    h->items = kh_init(heap);
+    h->items = kh_init(HEAP);
 }
 
 static void heap_finalize(Heap* h)
 {
-    kh_destroy(heap, h->items);
+    for (khiter_t k = kh_begin(h->items); k != kh_end(h->items); ++k) {
+        HeapValue value = kh_value(h->items, k);
+        switch (value.type) {
+            case TH_STRING:
+                free(value.value.str);
+                break;
+            case TH_ARRAY:
+                abort();  // not implemented yet
+                break;
+            case TH_TABLE:
+                abort();  // not implemented yet
+                break;
+        }
+    }
+    kh_destroy(HEAP, h->items);
 }
+
+static HEAP_KEY heap_add_string(Heap* h, const char* value)
+{
+    int ret;
+    khiter_t k;
+    HEAP_KEY key;
+
+    do {
+        key = rand();
+        k = kh_get(HEAP, h->items, key);
+    } while (k != kh_end(h->items));
+
+    k = kh_put(HEAP, h->items, key, &ret);
+    kh_value(h->items, k) = (HeapValue) {
+            .type = TH_STRING,
+            .value = { .str = strdup(value) }
+    };
+
+    return key;
+}
+
+#include <stdio.h>
+static TYC_RESULT heap_get_string(Heap* h, HEAP_KEY key, const char** value)
+{
+    khiter_t k = kh_get(HEAP, h->items, key);
+    bool is_missing = (k == kh_end(h->items));
+    if (is_missing)
+        return T_ERR_HEAP_KEY_NOT_FOUND;
+    *value = kh_value(h->items, k).value.str;
+    return T_OK;
+}
+
+static size_t heap_size(Heap* h)
+{
+    return kh_size(h->items);
+}
\ No newline at end of file
diff --git a/lib/tyche.h b/lib/tyche.h
index ba94516..8052146 100644
--- a/lib/tyche.h
+++ b/lib/tyche.h
@@ -8,6 +8,7 @@ typedef enum {
 typedef enum {
     T_OK = 0,
     T_ERR_STACK_UNDERFLOW = -1, T_ERR_STACK_FP_UNDERFLOW = -2, T_ERR_STACK_ACCESS_OUT_OF_RANGE = -3,
+    T_ERR_HEAP_KEY_NOT_FOUND = -10,
 } TYC_RESULT;
 
 #endif //TYCHE_TYCHE_H
diff --git a/test/tests.c b/test/tests.c
index 72b3de5..2c11110 100644
--- a/test/tests.c
+++ b/test/tests.c
@@ -92,5 +92,20 @@ int main()
         stack_finalize(&s);
     }
 
-    // TODO - stack set
+    {
+        printf("### Heap\n");
+
+        Heap h;
+        heap_init(&h);
+
+        HEAP_KEY key1 = heap_add_string(&h, "hello");
+        HEAP_KEY key2 = heap_add_string(&h, "world");
+
+        const char* value;
+        assert(heap_get_string(&h, key1, &value) == T_OK); assert(strcmp(value, "hello") == 0);
+        assert(heap_get_string(&h, key2, &value) == T_OK); assert(strcmp(value, "world") == 0);
+        assert(heap_get_string(&h, 1000, &value) == T_ERR_HEAP_KEY_NOT_FOUND);
+
+        heap_finalize(&h);
+    }
 }
\ No newline at end of file