Index scan is not working, why??

select *
from act
where act.acttype in ( 'Meeting','Call','Task');
  QUERY PLAN  
----------------------------------------------------------------------------------------------------------------------------------------
 Seq Scan on act (cost=0.00..13386.78 rows=259671 width=142) (actual time=0.013..484.572 rows=263639 loops=1)
  Filter: (((acttype)::text = 'Meeting'::text) OR ((acttype)::text = 'Call'::text) OR ((acttype)::text = 'Task'::text))
 Total runtime: 732.956 ms
(3 rows)

select *
from act
where act.acttype = 'Meeting'
or act.acttype = 'Call';
  QUERY PLAN  
----------------------------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on act (cost=17.98..1083.80 rows=2277 width=142) (actual time=1.901..9.722 rows=4808 loops=1)
  Recheck Cond: (((acttype)::text = 'Meeting'::text) OR ((acttype)::text = 'Call'::text))
  -> BitmapOr (cost=17.98..17.98 rows=2281 width=0) (actual time=1.262..1.262 rows=0 loops=1)
  -> Bitmap Index Scan on act_acttype_idx (cost=0.00..8.99 rows=1141 width=0) (actual time=0.790..0.790 rows=3181 loops=1)
  Index Cond: ((acttype)::text = 'Meeting'::text)
  -> Bitmap Index Scan on act_acttype_idx (cost=0.00..8.99 rows=1141 width=0) (actual time=0.469..0.469 rows=1630 loops=1)
  Index Cond: ((acttype)::text = 'Call'::text)
 Total runtime: 14.227 ms
(8 rows)


\d act
  Table "public.act"
  Column | Type | Modifiers  
------------------+------------------------+-------------------------------------------
 actid | integer | not null default 0
 subject | character varying(250) | not null
 semodule | character varying(20) | 
 acttype | character varying(200) | not null
 date_start | date | not null
 due_date | date | 
 time_start | character varying(50) | 
 time_end | character varying(50) | 
 sendnotification | character varying(3) | not null default '0'::character varying
 duration_hours | character varying(2) | 
 duration_minutes | character varying(200) | 
 status | character varying(200) | 
 eventstatus | character varying(200) | 
 priority | character varying(200) | 
 location | character varying(150) | 
 notime | character varying(3) | not null default '0'::character varying
 visibility | character varying(50) | not null default 'all'::character varying
 recurringtype | character varying(200) | 
 end_date | date | 
 end_time | character varying(50) | 
Indexes:
  "act_pkey" PRIMARY KEY, btree (actid)
  "act_acttype_idx" btree (acttype)
  "act_date_start_idx" btree (date_start)
  "act_due_date_idx" btree (due_date)
  "act_eventstatus_idx" btree (eventstatus)
  "act_status_idx" btree (status)
  "act_subject_idx" btree (subject)
  "act_time_start_idx" btree (time_start)

Any idea please.